Chap. HI. 



GENUS IDYIA. 



283 



send off along their whole course innumerable branches, ramifjdng in the thickness 

 of the spherosome (PL II. Fir/. 10). These ramified tul:)e,V everjAvhere visible through 

 the transparent spherosome, give it a very peculiar appearance, as if made up of 

 irregular meshes. Nothing of the kind is seen in any other type of CtenophoriB. 

 The coeliac tubes alone are simple, and do not give oft' or receive any branches. The 

 origin and ramification of the minor tubes pervading the spherosome present some 

 striking peculiarities. Those of the anterior and lateral interambulacra {Figs. 1 and 2), 

 running nearer to the surface and consisting of thinner Ijrunches, arise from the 

 ovarian side of the ambulacra! tubes, and, in flict, are direct prolongations of the 

 ovisacs ; while those occupying the anterior and the posterior pairs of interambulacra 

 have a deeper origin, from the inner side of the 

 ambulacral tubes, and, bending over the spermatic sacs, 

 ramify nearer the inner surface of the spherosome, and 

 are, on the Avhole, Avider than the others (PI. II. Fi(j. 1(1). 

 Fig. 99, which gives a transverse section across the 

 middle of the body, shows the origin and distrilaution 

 of these different branches, and makes it evident that 

 none arise, either from the side of the spermatic sacs 

 or from the coeliac tubes. 



Fig. 10, PI. II., representing a vertical section of 

 the whole animal nearly to the abactinal pole where 

 the spherosome is cut transversely, gives the best 

 idea of the ramifications of the chymiferous tubes on 



the inner surfiice of the spherosome, and shows how 

 much they differ on that side from those on the ex- 

 ternal surflxce (PI. I. Fig. 1). Fig. 100 is a reproduction 

 of the abactinal part of Fig. 10, PL II. Along its mar- 

 gins are seen one of the anterior and one of the 

 posterior ambulacral tubes for their whole length, the 

 corresponding tubes /" /^ {Fig. 100) of the opposite side 

 being cut through. In the centre is the large coeliac 

 tube of one side, and its corresponding tube of the 

 opposite side r is cut through. The two lateral aml^u- 

 lacral tubes of one side arc also seen for their Avhole 

 length, and the corresponding tubes of the opposite side. 

 Between the abactinal end of these branches the short but 



Idyla roseola, Arj. 



Transverse section across the middle of the 

 body, 

 rri coeliac tubes. — 1^1^, l^l^ lateral tubes. — l-l^^ 



}}'> n anterior and posterior tubes. — o o ovaries. 



— 5 5, 5 5 spermaries. — 1 1 internal ramifications 



of the anterior and posterior tubes.— t^ internal 



ramifications of the lateral tubes. 



Fiff. 100. 



Idtia roseola, Ag. 

 r ri coeliac tubes, r is cut near its origin. 



3^1 lat- 



eral ambulacral tubes cut near their origin. —^^ t^ 

 anterior and posterior ambulacral tubes, cut near 

 their origin ; all the cut ambulacral tubes are on 

 the same side of the body ; on the opposite side 

 the following organs are visible from their internal 

 face : — ?<> l^ anterior and posterior ambulacral 

 tubes. — l^l^ lateral ambulacral tubes. — a a a a 

 represents the section of the spherosome. 



P l^, are cut through. 



^ Among some Echinodcrms tliere is something 

 quite similar to these ramilieations of the ambu- 



lacral tubes ; for I do not douljt that the tube 

 extending throushout the thickness of the shell of 



