Mr Menon, Notes on Semper s Larvae. 411 



The syncytium presents a new appearance. The central portion 

 has separated off from the peripheral and lies in a central cavity into 

 which the stomodaeum opens. In sections passing through the oral 

 half of the larva this central portion is not seen ; in this region, 

 therefore, the mass has already broken down, giving place to a 

 cavity which occupies the whole of the interior of the larva. The 

 vacuolated peripheral portion of the syncytium containing a little 

 yolk becomes the endoderm. The central portion, which is also 

 vacuolated and contains yolk, has quite disappeared in the follow- 

 ing stage, having, no doubt, been resorbed. In this stage, a section 

 of which is shown in fig. 7, the central cavity is lined by a 

 vacuolated endoderm layer containing scattered nuclei and small 

 rounded granular masses of yolk. The endoderm thus apparently 

 does not at any stage consist of regularly arranged cells like the 

 ectoderm, but is from the beginning a vacuolated syncytium which 

 in later stages becomes enormously developed and fills up the 

 greater part of the coelenteron. 



The coelenteron thus arises by the splitting of the inner mass 

 and becomes definitely established by the breaking down and 

 resorption of part of that mass. 



In the stage represented in fig 7, along two opposite lines of 

 the coelenteron, the nuclei of the endoderm lie close together, and 

 here the endoderm (as far as can be made out from the longitu- 

 dinal section) projects in the form of two irregular ridges into the 

 coelenteron. They are, no doubt, the beginnings of the first pair of 

 mesenteries. The mesenteries are thus formed at an early stage 

 and before the others. The stomodaeum is quite well marked and 

 its epithelium is of the same nature as the outer ectoderm. I 

 have not noticed in the ectoderm of the earlier stages the pigment 

 cells found in the late stage. 



I obtained several specimens of Semper's second larva which, 

 I believe, is the one named Zoanthina by Van Beneden. The 

 youngest specimen (fig. 8) measured about § mm. and the oldest 

 over 3 mm. in length. I have not found any specimens of this 

 larva associated together in the curious manner described by Van 

 Beneden — younger stages occurring within the body of an older 

 stage. 



The form of the larva varies from time to time. Its usual 

 appearance as it lies on the bottom of the glass vessel is that 

 shown in fig. 8. Often it assumes a more elongated club-shaped 

 or subcylindrical form. The colour varies ; it may be light-brown 

 or dark-brown or slightly yellow, or the larva may be almost 

 colourless. The colour seems to depend to some extent on the 

 amount of coloured yolk in the endoderm. Light streaks running 

 along the outside of the larva mark the attachments of the mesen- 

 teries, which are also made evident by shallow external grooves, 



