its limbs that exposure of the under side to the attacks of fishes would soon end its career. In short it must keep its carapace "right side up with care," if it would care to live.

Intended for
Their use is

I must now mention another functional metamorphosis which seems to me of a very remarkable character. So great is the difference in form between the anterior feet of the female, and the same feet in the male, that the very children on the shore lines at once in this way distinguish the sexes. In the female this limb is long, slender, and weak; in the male short, stout and ventricose. strong holding, their nip is like that of a vice. to hold on to the carapace of the female, so that the male may retain his position as the pair come up in the breeding season. And so strong his hold that no violence of storm, or attack of rival suitors, can displace him. Well does the fisherman know this, as he stands in the water ready to spear the female as she comes up in nuptial embrace. He is only concerned to catch the female, for it would need some force to separate the two. Now functionally, this stout foot, "or hand," as the fishermen call it, has no use in early life. The Horse Foot Crab has its period of puberty; this is its adult stage. But judging from the size of the males when they couple, which is pretty uniform, and their actual rate of growth, I think that the puberty of Limulus cannot come before the third or fourth year. And it would not surprise. me if the latter figure should prove the minimum age. However this is the point-it is not until that age of puberty is reached that the male undergoes its last metamorphosis. It then has a moult, from which it emerges, having received its large claws, or literally, its nuptial hands. What change there may be on the emotional side who can tell, when master Limulus assumes the toga virilis and is old enough to "propose." This may be asserted of these very decorous and monogamous people, that among them premature marriages are unknown, for however soon the lady may be ready to give her heart, not until maturity of age can the gentleman possibly extend to her his hand.

The above fact was obtained by evidence purely negative, yet not the less convincing. First, there was the suspicion of the fact, then the search for a young male possessing nuptial claws. But albeit the numerical equality of the sexes this was not found, though large numbers of young specimens of different ages were examined. Moreover, I have not found the fisherman who has ever seen one.

Although some of the systematists make of Limulus a distinct order, as Xiphosura, or sword-tailed; yet I cannot but think that in nature the Trilobites are included, making of all one grand order. It would thus have not only a real systematic meaning, but a profound chronologic significance. However this may be in the light of coming knowledge, I think Pterygotus and Eurypterus stand higher than the typical Trilobite proper, and that Limulus leads rank over all.

Figure 68 shows Limulus after the first moult (very much enlarged), when not more than a week old. The fringe of the buckler is now less thickly set, the cardinal spines only being conserved, and these not so stout.

The

posterior shield shows the permanent spines. Still the contour is asaphoidal while the median ridge of the abdominal carapace, terminating in the point of the mucronated shield, is suggestive of the dorsal keel in Pterygotus gigas

Fig. 68

and P. anglicus. At this stage, as the Limulus after the first moult. facts seem to me, the larval Limulus shows forth more than one generic "expression point" in the career of the trilobite as a "comprehensive type."

It should be stated here that the exuvia represented by fig. 68 was accidentally discovered on the surface of the mud, at the bottom of an hatching jar, used in these observations last summer. At the close of the warm season last year my jars must have contained not less than two hundred young Limuli. We have already said that so

soon as

hatched the young burrow like the adult; hence the rareness of an opportunity to witness the casting of the skin. Hoping to continue observations upon the growth of my interesting family the ensuing year the jars were carefully put away. Little regard, however, was paid to temperature, which, on several occasions, went down to the freezing point. On the 3d of May, 1870, I emptied the jars to see how my charge was getting on, when lo, not one of the last year's hatching was alive! but wonderful to say at least a dozen little fellows, all hatched this spring, and all alive, had taken their place. With these were also at least thirty eggs, in different, but all in advanced, stages of incubation. In some of them the young could be plainly seen revolving. The fact was these eggs had been at the bottom of the hatching jar, and had never had any contact with the sunlight. At once, not without some misgiving as to the result, the proper provision was made to complete the incubation, namely, new sea-water, clean sand, the eggs put on top, and all set in a favorable place. With an ordinary hand lens the progress of incubation could be observed daily. At half-past four o'clock on the afternoon of May 11th, before my eyes, a new-born baby Limulus left the egg. Just think of it-these eggs are within two weeks only of being a year old! And then how remarkable are these facts also-those eggs were partly incubated last summer. Hence there has been not only a remarkable retardation of development, but also an actual arrest of the same for seven or eight months without sacrificing life. Query: is there any connection here with that indomitable persistence of being, which in the Divine will has carried this comprehensive type through the many EONS of existence, wherein has been unrolled so slowly the life plan of the Entomostraca, from that initial Trilobite of the Pre-siluria to our Limulus of these latter days?

It has been hinted already in this article that at different stages of its life the larval Limulus made a different impress