66 



PROF. AGASSIZ S 



[PLATE XIX YOUNG CRABS, SHRIMPS, BARNA- 

 CLE AND CYPRIS 1 



We may say the same of Barnacles, in which in 

 the final condition there is nothing of Crustacea in 

 their external appearance; but which when young 

 resemble common Shrimp-like Crustacea, to a very 

 great extent, as we see by comparing a Cypris. 

 (Plate XIX. fig. F, with a young Barnacle, fig. G). 

 There are several of these horn-shelled Crustacea 

 which have been described as peculiar animals ; 

 for instance, the species figured, which constitute 

 the genera Foda, Megalopa and Cuma, (Plate XIX, 

 tigs. A, B, C, D, E ) which are nothing but young 

 Crabs and Shrimps. Their resemblance to Cyclops, 

 or Calanus, (Plate XVI II, fig. F,) or to Cypris, 

 (Plate XIX, fig. F) is however striking. Here is a 

 species (Plate XIX, fig. F) of Cypris, for instance, 

 which resembles, not only the other young Crusta- 

 cea of figs. A, B, C. D, E, but even the young 

 Barnacles (Plate XIX, fig. G) most remarkably. 

 The young of a shelly animal, which in this early 

 condition of life is a little, free, moving Shrimp-like 

 Crustacean, with an elongated tail, with legs and 

 respiratory fringes, having eyes in the anterior 

 portion of the body,which is similar, in fact, to other 

 young Crustaceans, and which, after it has grown 



to a certain size, becomes attached, and is trans- 

 formed into the remarkable Barnacle. Here are 

 some more, of the curious Entomostraca (Plate 

 XX) to which I shall call your attention. We have 

 (Figs. A to E) one species, (Figs. F to K) another 

 species. This latter one, resembles the Lernea in 

 many respects ; being attached by a sucker to the 

 gills of fishes, on which they live, but having still 

 a proboscis with jointed appendages, and having 

 also indications of rings in the posterior part of 

 the body, and having sacks of eggs hanging be- 

 hind. In the other, Apus, (Figs. A to L) the body 



PLATE XX ROTIFERA, AND 



TACEA ] 



PARASITIC CRUS- 



