an active little creature, having more resemblance to a cray-fish or lobster than to its parent crab. It crawls with considerable rapidity over the muddy and sandy sea-bed in shallow water; or swims in shoals or streams, of two feet or more in width, with great regularity and precision of movement. Each beside the other swims with steady stroke, near the surface, and leading in one direction, usually towards the deeper water.

Its body is whitish translucent, glistening, and the shell so thin as to be almost transparent. Its eyes are very bright blue, and being quite large heighten the pleasing effect of its appearence as it moves through the water. The head is almost quadrangular, raised like a tablet, with the front margin triangular and provided with a long slender stylet, projecting forward from the centre. The carapace is strikingly different from that of the older crab; it is long-quadrangular, raised above the level of the abdomen, and the sides are rounded off and slightly sloping towards the under side. Its four pairs of hind legs resemble those of the adult, except in the last joint of the posterior pair, which is not widened into a broad paddle, but, while being of the shape of a sword-blade as the others, is a little more expanded, and adapted both for swimming and creeping. Besides this the tip of each foot is provided with a slender spine, which enables the creature to hold firmly to any object upon which it may alight.

The abdomen stretches back long and narrow, a little tapering towards the tip, not having the tail expanded as in the lobster, but with the end piece long-quadrangular, a little rounded behind, and terminated by a few slender threads.

Vast numbers of this Megalops were observed by me on the fourth day of this month in places where the female Callinectes was incubating. A few Zoeas were in the swarms, and I was enabled to secure a large supply of specimens. The muddy sand was crowded with them around the female crabs, so that stirring of the bottom set them streaming in every direction. They were observed in many places, both at an earlier and later date, but never in such remarable swarms as on that occasion. The weather had then been calm for several days, and the remarkably hot season no doubt favored their developement. They generally measured 3 millemetres in length, by 1 millemetre in width, while the abdomen was scarcely more than a half millemetre in width.

This crab not only contributes to the sustenance of man; it forms the most abundant food of a great proportion of the other tenants of the seas. Perhaps no creature of the water multiplies in such countless swarms. Were it not for the great number of enemies which are ever on the alert to devour it, the sea might be crowded so full of crustacean forms as to leave no room for other animals.

However, it is probable that not the one-hundredth part of the ripe females are able to remain undisturbed long enough to hatch their eggs. Skates, Rays and other monsters of the deep are continually searching for them, and nearly all the varieties of our larger food-fishes pursue them to destruction. The patient females hide in the sea-weed or bury themselves in the mud to escape their persecutors, but rarely do they succeed in evading them. When aroused they may protect themselves and eggs with savage energy, but in general they remain so quiet as to be touched by the foot without causing them to show signs of irritation.

PHILIP R. UHLER.

Sexual Variation in the Genus Leucosticte.

In Mr. Ridgway's recent reply to my critique † upon his "Monograph of the Genus Leucosticte," he states, very truly, that "the point at issue is, whether the sexes of tephrocotis' and 'littoralis' do, or do not, differ in plumage," and, he should have added, in size. Having shown, in my above-cited paper, that there exists in these forms the usual amount of sexual variation in size found in this genus, and that there is also a well-marked sexual difference in color, Mr. Ridgway attempts to avoid a full admission of the correction by saying that this, "in a diagnostic sense, means whether there are, or are not, absolutely constant sexual differences!" Under the heading Under the heading "Sexual Differences," Mr. Ridgway, in his Monograph, says: "The American species of this genus fall into two distinct groups according as the sexes do or do not differ in appearance. In L. tephrocotis-in all its formsthere is not the slightest sexual difference §; but in L. atrata and L. * This Journal, September, 1870.

+

+ Bull. U. S. Geol. and Geog. Survey of the Terr., Vol. II., No. 4, pp. 345-350. Ball. U. S. Geol. and Geog. Survey of the Territories, 2d Ser., No. 2, p. 60. Not italicised in the original.

australis, the distinction is very marked." Without attempting to squarely meet this issue, he calls attention to supposed differences in the character of the specimens constituting our respective series, remarking that while his series "embraced both forms in very dissimilar Winter and Summer dresses," mine "embraced only Winter specimens." As a "matter of fact," however, mine were collected (as shown by the collector's labels,) at different times from November to March 11, while his latest published dates are March 20 to 25 for tephrocotis, and March 10 and April 18, (single specimens each) for littoralis.

The main point at issue being substantially conceded by Mr. Ridgway, I will say but a word or two on minor points. In respect to my still regarding all the forms of Leucosticte as "intergrading forms," Mr. R. labors under a grave misapprehension. The main subject of my paper being sexual variation in two varieties of L. tephrocotis, I very naturally entitled my article "Sexual, Individual and Geographical Variation in Leucosticte tephrocotis;" but I see nothing in the article that need to lead to the supposition that I accorded any of them, except L. " atrata," a different rank from that which Mr. Ridgway claims for them in his Monograph. On the contrary, I intended to imply, by adopting, without reservation, (by the use of quotationmarks or otherwise, Mr. Ridgway's nomenclature, that I did admit all except L. " atrata," in the same sense as did Mr. R., himself, and trusted that I had made that fact evident. I regret that he has been so far misled as to feel called upon to re-argue and re-affirm the specific and varietal rank of the other forms, or that he should feel warranted in assuming that the views I expressed four years since have been unmodified by the subsequently greatly increased knowledge of the different forms of this, at that time, little known group. Perhaps I may be allowed, in this connection, to remind Mr. Ridgway that he would not, at that time* admit even the varietal distinctness of L. australis from L. tephrocotis proper, while at the same time L. campestris was so recognized by him, and so retained two years later when L. australis was formerly introduced as a "variety." I may add that it was partly in deference to the opinion of Mr. R. and other well-known

* See Baird, Brewer and Ridgway's Birds of North America, Vol. I, p. 504, foot

note, 2.

Ibid., Vol. III, p. 509.

66

Washington ornithologists that led me to regard L. australis as representing only the breeding dress of the Southern form of L. tephrocotis, after I had gone so far as to formally describe it as a variety, making the suppression in my last revise of the proof-sheets of that part of the "Ornithological Reconnoisance." With my specimens before them, the authors of " North American Birds" say that "it seems very reasonable to suppose that these specimens represent the breeding plumage of that [L. tephrocotis] species," the theory I at first entertained and finally adopted. It thus appears that even Mr. Ridgway's opinions have considerably changed in four years, respecting the character of the "different forms" of Leucosticte. He ignores, however, the fact that one of the forms (L. campestris") to which I referred in 1872, as possibly founded on individual variation, he himself, in 1875, regarded as "unstable as a race, from the fact that scarcely two specimens are alike." Mr. Ridgway's commendable acuteness in recently relegating certain specimens, from my description of them in 1872, to his several species and varieties, results from the examination of a large amount of material not accessible to any one at the time I wrote. L. "atrata" is now the only "form" of Leucosticte, respecting the character of which we now differ, and this, Mr. Ridgway admits is "possibly, but but not probably a melanism of L. tephrocotis." The apparent difference between us on the subject of species and varieties in this group results simply from his choosing to quote my opinions of 1872 as being those of 1876.

In saying that the measurements, given in my late article, (1. c., pp. 349, 350,) “were made by the collector from fresh specimens, and as the sex of each specimen was determined by actual dissection, they are of special interest in the present connection," I intended no reflection whatever upon the "experience" and "veracity" of Mr, Ridgway's correspondents, the remark having the most evident allusion to the fact that in only a relatively small proportion of the specimens of which he gave measurements was the sex indicated.

The sweeping charge Mr. Ridgway brings of the almost total unreliability of my scientific work I do not feel called upon to further notice, the spirit animating his whole article being in itself a sufficient reply. Yet I may thank Mr. Ridgway for thus giving me a favorable

In his last notice of the group, (this Journal, September, 1876,) he raises L. griseinucha from a "variety" of L. tephrocotis to the rank of a distinct species.

opportunity of referring to one or two other matters. In the "Mammals and Winter Birds of East Florida," I freely confess to having too hastily formed conclusions "regarding the relationship of certain congeneric forms" in several instances among the Falconida, and in one or two other groups, (Bucephala and perhaps in Centurus,) and that I made a mistake in respect to Pipilo macronyx, but the question of whether certain forms referred to are "species" or merely "geographical races" does not seriously affect the points then under discussion. Probably there is still a difference of opinion between Mr. R. and myself, respecting several of the components of the groups in question. The case of Peucæa " Cassini," however, is somewhat different, as is shown by the following quotation from "North American Birds," (Vol. II, p. 43,) published two years after the occurrence of the alleged gross blunder. In the above-named work it is stated that "the general acceptance of the name Cassini has been that of a term designating a variety of the common species,"-which is just the sense in which I used it, the discovery of the impropriety of which had not, at that time, been made public.

Mr. Ridgway, perhaps I may be allowed to add, has had to correct his own "hasty conclusions," or has had them pointed out by others, quite too often for such criticism to come with very good grace from his pen.

J. A. ALLEN.

Vegetable and Animal Cellulose.

In each of the monthly reports of the Department of Agriculture for July, 1875, and May and June, 1876, appears an article on the subject of cellulose, both vegetable and animal. The first article relates mostly to the discoveries and observations of the scientists of Europe on animal cellulose, and the second to experiments based on them, together with others made by myself with their results, being really a continuation of the original observations of Virchow. Any person who has given this subject full consideration will comprehend the scope and tendency of these investigations. If it can be shown, to a demonstra tion, that vegetable cellulose is a constant constituent in the organs and blood of the higher animals, including man, we establish the fact