380 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



AH abridged larval development Las been attributed to the following macroura: The lobster 

 JiomariiH americanus; the crayfishes ; Rippolytc polaris; Palmnoneles varians; Palwmon potiuna ; Pa- 

 la-mon rt//.v/jfi/".w.v and Eriphia. apinifrons (as first observed by Eathke, according to Packard) ; Bytlia- 

 cinifi Inicopftls (observed by G. O. Sars, according to S. I. Smith) ; Alpheus heterndtflix, and A. snvlcyi. 

 To this list we must probably add the names of many deep-sea decapoda, Muniilopsix, Glypho- 

 cratiyon, ElnsmonittHx inermis, Sabinea princepx, Acantliephyra gracilis, and Pnsiphuc prlmeps, as 

 inferred by S. I. Smith, on account of the extraordinarily large size of their eggs. An egg of 

 remarkable dimensions is that of " the little shrimp (Pampiisipluii 1 xiilcalifron*,) which carries only 

 lifteen to twenty eggs, each of which is more than 4 millimeters in diameter, and approximately 

 equal to a hundredth of the bulk of the animal producing it a case in which the egg is relatively 

 nearly as large as in many birds! " "Although the great size of the eggs," says Prof. Smith, " is 

 highly characteristic of many deep-water species, it is by no means characteristic of all, and the 

 size of the eggs has no definite relation to the batliymetrical habitat, and is often very different in 

 closely allied species, even where both are inhabitants of deep water (59)." 



The larval life of both terrestrial and fresh-water Crustacea is generally short as compared 

 with that of marine forms, and the case of the crayfish may find an explanation in the well-known 

 law that fresh-water life tends to shorten the development, as is shown in a remarkable manner in 

 the fresh-water variety of Palrvmonctes rarinn.t, described by Boas (4). Why, on the other hand, 

 it is beneficial for the lobster to abbreviate its larval development is not plain, since its young at 

 the present time hatch apparently under the same conditions as other pelagic larvre, and, like 

 them, swim at the surface of the ocean. S. I. Smith (58) and .Ryder (55) have given accounts of 

 the larval history of the lobster. (Since this paper was written I have undertaken a revision of 

 this subject, and the results will be given in a fully illustrated report to the United States Com- 

 missioner of Fish and Fisheries.) While tin's animal hatches in a precocious state its life at the sur- 

 face is by no means short, since, according to Ryder, it ordinarily requires seven weeks to pass 

 through six molts. The first larva hatches in a schizopod stage, but there are no abdominal legs 

 and the antennae are somewhat rudimentary. The first ecdysis, according to Ryder, does not occur 

 until from three to six days after hatching.* It is in the second stage that the second to fifth 

 pairs of abdominal appendages make their appearance. 



The third stage is preceded by a molt ten to fifteen days after hatching, and now the append- 

 ages of the last abdominal segment are formed. After the fourth molt (fifth stage) the young 

 lobster, now 14""" long, quite closely resembles the adult. It swims more on the bottom. The 

 llagella of the antenna? are equal to the cephalo-thorax in length. The exopodites of the thoracic 

 legs are reduced to bare rudiments. The chelipeds show adult characters. The first pair of swim- 

 merets are developed in the seventh stage, at the end of which there is a decided difference between 

 the great claws. 



It will be seen that the fifth stage in Ryder's account, attained at the end of the third week, 

 nearly corresponds with the third larva of Alplicus saulcyi (Fig. 8, PI. xxi) as it appears twenty-four 

 hours after hatching, but the latter has the more decided adult characters. The young Alpheus 

 is further advanced than the lobster at the time of hatching and reaches maturity in a remark- 

 ably shorter period. 



Boas calls attention to the fact that while the young of the salt and fresh water forms of 

 Paltemonetes i-ni-innx are very different, the adults of these two varieties resemble each other very 

 closely. Much more remarkable is the case of Alpheus hetcrochelis, even if we regard the Nassau 

 form an a. distinct species, and that of Alpln'iix unnlci/i, where we have the same species living in 

 the. same sponge, hatching now as a larva and now as a form possessed of all the external adult 

 characters. 



Both the long and short metamorphosis has been attributed to the West Indian shore crab 

 Gegardnus. This highly colored crab (Gef/nrchnix ruricola) is very abundant at Nassau, and from 

 its exceptionally large egg we may safely infer that the development has here been shortened. 

 Fritz Mtiller (42) has found abbreviated development in the South American crabs, Tricliodactylw 

 and -Eflle.a ("mountain crab"). 



"A delicate moulted skin, which is easily overlooked, cither comes oft" with the egg membranes at the time of 

 hatching or is shed shortly after, as my own observations have clearly shown. 



