276 CTENOPHOR^. Part II. 



mentioned, the rows of locomotive flappers extending only over a limited part of 

 their surface {Fig. G and magnified Fig. C), but they are also more romided, the 

 sides not being so flattened as in the adults. Moreover, the flappers iu each row 

 are fewer, and, comparatively to the size of the body, much longer, than in the 

 adults, and the rows themselves much further apart. The chymiferous tubes, which 

 penetrate like a network through the whole thickness of the spherosome, are also 

 much fewer and much less branching in the young than in the adult. Again, before 

 the spawning season approaches, the color over the whole surface is more uniform 

 and paler, as in Figs. 7 and 8, the ovaries and spermaries being not yet visible ; 

 while in the adult {Figs. 1, 2, and .3), they appear as bright rows of branching 

 sacs on the sides of the aml:)ulacral tubes. The arrangement of these organs is 

 so peculiar that it increases the differences resulting already from the inequality 

 of the spheromeres, the ovaries forming broader sacs, of a paler color than the 

 spermaries, which are accompanied by more intensely tinged pigment cells. And 

 then, owing to the fact that alternate interambulacral zones are occupied by ovaries 

 and spermaries, each ambulacrum has ovaries on one and spermaries on the other 

 side of its amljidacral tu)je, so that, though each ambulacrum is more jjrightly colored 

 than the intervening space, it is paler on one side than on the other, the pale 

 sides, occupied by the ovaries, being always turned toward each other, as are the 

 bright sides also, which are occupied by the spermaries {Figs. 1, 2, and 3). But 

 none of these differences are visible in early life. Again, when well fed the outlines 

 are rounded {Fig. 3) ; 1nit after fasting the interamlnilacral zones subside and the 

 ambulacral zones become prominent {Figs. 1 and 2). 



In the plates representhig Idyia roseola I have attempted to reproduce the 

 appearance of all the parts of the animal as nearly as possible like life, and have 

 been assisted iu this attempt beyond my expectation by the skill of Mr. Sonrel. 

 But so delicate is the substance of this animal, and so slight are the outlines of 

 its different parts when seen through the thickness of the spherosome, that they 

 could only l)e faintly represented, in order not to exaggerate their natural apjjear- 

 ance. Upon careful examination of the figures of Plates I. and II. it may, however, 

 be found, that, fixint as they are, the outlines of all the organs are correctly rendered. 

 Yet, to obviate the difficulty that may arise in comjiaring the descriptions with 

 these plates, I have had wood-cuts made of the most characteristic details of the 

 structm'e, corresponding to the colored plates and explanatory of them. Fig. 10 

 of PI. II. is the only one in which the structural details are reproduced with a 

 dark tint which they never had in nature. As already stated when characterizing 

 the family of the Beroids proper, our Idyia has the spherosome of a very uniform 

 thickness, though the spheromeres are not perfectly equal in their size. The anterior 

 and the posterior pairs are somewhat nearer to one another, and their lateral 



