MEMOIRS OF TOE NATIONAL ACADEMY OV SCIENCES. 



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These two forms, altliough apparently distiuct. are seen, however, by closer study to belong to 

 the same species; but besides the more sui)erficial 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, Alpheiix .snulcyi, Guerin, it is necessary, for descrii)tive purposes, to distin- 

 guish two varieties, viz : 



Alpheus sanlcyl, variet3' longicarpus (from brown sponges), 

 Alphens mulcyi, variety brcricarpus (from green sponges). 



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

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

 profouud variations mentioned in section v), while the brevicarpxig type from the green spouges 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-i>rotection, 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 i)laces of concealment, recall the similarly colored heads 

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



It seems (juitc probable that if we have in this Alphens a case of protective coloring, it is due 

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

 not appear in any of the species of Alphens 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. Iu the Alphens, parasitic in the brown sponges, these colors vary cousid- 

 eraldy 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 difiereutly 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 Alphens hetfrochclis are almost invariably of a dull olive color, while, as in 

 the case of the parasite of the green spouge, 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 iu 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. 



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

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



* A parasitic Isopoil, probably a Bnpyrus, is foand on both tlie varieties, bnt is ijiost common with the dweller in 

 the brown sponge. It appears aa a tumid buncb, firmly rooted in tUo br.ancliial cavity or to the under side of the 

 abdomen. In this connection I will mention another curions par.osite which was found infesting the eggs of a single 

 female taken from a brown spouge at Abaco. This is a large, s])lierir:il, nnicellnlar organism in the encysteil state. 

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



In looking over .a collection of unpublished ilrawings of Crust.acea, ni.ide by the associates of Louis Agassiz and 

 deposited iu the library of the Museum of Comparalivi- Zoology of Ilarvaril College, I find a sketch (by H. J. Clark, 

 December 23, 18,">7) of a Bopijrus taken from the branchial cavity of Aljiheus heterochelis. 



