MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



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These two forms, although apparently distinct, are seen, however, by closer study to belong to 

 the same species; but besides the more superficial variations just mentioned, there are others of a 

 more remarkable character, the morphological significance of which is considered in sections IV 

 and v. 



Of this species, Alpheus saulcyi, Guerin, it is necessary, for descriptive purposes, to distin- 

 guish two varieties, viz : 



Alpheus saulcyi, variety longicarpus (from brown sponges), 

 Alpheus saulcyi, variety brevicarpus (from green sponges). 



These two varieties shade completely into each other by numerous intermediate forms. The 

 longicarpus varies greatly in size and in the color of the body and eggs (besides the other more 

 profound variations mentioned in section v), while the brevicarpus type from the green sponges is 

 more uniform in size and stable in color and other characters. The former variety is well pro- 

 tected from outside enemies while in the tortuous mazes of its sponge, as its great numbers would 

 show, if any evidence under this head were needed. The enemies which invade them successfully 

 seem to be parasites.* 



Possibly the variety inhabiting the green sponge does require color-protection, especially since 

 the females are very inert during the breeding season. They are, indeed, admirably protected 

 when exposed on the green surface of sponges, alga;, etc. The bright color on the tips of the large 

 claws, which only are protruded from the places of concealment, recall the similarly colored heads 

 of boring annelids, which abound on the reef, but this fact may have no significance. 



It seems quite probable that if we have in this Alpheus a case of protective coloring, it is due 

 very largely to individual adaptability. This view implies great individual plasticity, which does 

 not appear in any of the species of Alpheus known to me within- a restricted area. 



The colors of certain Crustacea, and also the colors of their eggs, are known to vary greatly 

 with the surroundings. In the Alpheus, parasitic in the brown sponges, these colors vary consid- 

 erably where the surrounding conditions are the same. However, the color of the ovarian eggs is 

 always the same as that of those already laid, and, although these animals were kept for several 

 days at a time in differently colored dishes, I never observed any very marked change in the color 

 of the ovary, but these experiments were not continued long enough or carefully enough to be con- 

 clusive. The eggs of Alpheus heterocJieUx are almost invariably of a dull olive color, while, as in 

 the case of the parasite of the green sponge, about one in a hundred has bright yellow eggs. In 

 the first case at least this may possibly be an instance of reversion to one of the. original colors 

 from which the green was selected. In most species of Alpheus the color of the eggs is fixed and 

 uniform for any locality, and, as already suggested, may have a protective significance; but in a 

 few other cases, where this is not true, the color is not only variable in different individuals, but 

 probably also in the same individual. 



Alpheus heterochelis from Beaufort, N. C., is uniformly of a dark olive-green color, with some 

 red and blue on the appendages. It lives iu the beds of oyster shells, which are more or less 



*A parasitic Isopod, probably a Hop?/ run, is found on both the varieties, but is most, common with the dweller in 

 the brown sponge. It appears as a tumid bunch, (irmly rooted in the branchial cavity or to the tinder side of the 

 abdomen. In this connection I will mention another curious parasite which was found infesting the eggs of a single 

 female taken from a brown sponge at Ab.ico. This is a large, spherical, unicellular organism in the encysted state. 

 The egg, with the embryo, is packed full of them. (v. Fig. I'M and section IV, Part Second.) 



In looking over a collection of unpublished drawings of Crustacea, made by the associates of Louis Agassiz and 

 deposited iu the library of the Museum of Comparative Zoology of Harvard College, I find a sketch (by H. J. Clark, 

 December 23, 18f>7) of a Bopyrut taken from the brauchial cavity of Mjiheus helerochflis. 



