380 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



An abridged larval developmeut Las been attributed to tlie following uiacroura : The lobster 

 Homarns americanus ; the crayfishes; Hippolyte polaris ; Pakemoneies varians; Pala'inon potiuna; Pa- 

 Iwmon aflspersus and Eriphia spinifronH (as first observed by Ratbke, according to Packard) ; Bytho- 

 earis lexicopsis (observed by G. O. Sars, according to S. I. Smith) ; Alpheus heterochelis, and A. naiilciii. 

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

 crangon, Elasmonotus inermis, Sabinea princeps, Acanthephyra gracilis, and Pn.siphai'' princeps, 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 [Parapasiphad sulcatifrons,) which carries only 

 fifteen to twenty eggs, each of which is more than 4 millimeters iu diameter, and approximately 

 equal to a hundredth of the bulk of the animal i)rodiicing it — a case in which the egg is relatively 

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

 Iiighly 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 bathymetrical habitat, and is often very different iu 

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



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

 with that of marine forms, and the case of the crayfish m.iy fijid an explanation iu 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 Palwmoiietes varians, 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 larva*, and, like 

 them, swim at the surface of the ocean. S. I. Smith (58) and Kyder (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 iu a fully illustrated report to the United States Com- 

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

 face is by no means short, since, according to Eyder, 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 antennse 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 fourtii molt (fifth stage) the young 

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

 flagella of the antennai 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- 

 raerets are develoijed 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 corresiionds with the third larva oi Alpheus 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 

 Palwmonetes varians are very different, the adults of these two varieties resemble each other very 

 closely. Much more remarkable is the case ot' Alpheus heterochelis, even if we regard the Nassau 

 form as a distinct species, and that of Alpheus saulcyi, where we have the same species living iu 

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

 <:haracters. 



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

 Gegarcinus. This highly colored crab {Oegarcinus ruricola) is very almndant at Nassau, and from 

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

 Fritz Miiller (42) has found abbreviated development in the South American crabs, Triclmdactylus 

 and ^J/^/Zfirt ("mountain crab"). 



* A delicate moulted skin, whicl] is easily overlooked, either comes oflfwith tbe egg moiubranes at the time of 

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



