3l8 McMURRICH. [Vol. IV. 



which I find in a limited number of preparations ; a more com- 

 plete series is necessary to determine accurately the actual 

 occurrences. We have, however, a description of a more ample 

 series of embryos of Manicma, by H. V. Wilson (['i^), and this 

 furnishes a basis for understanding more disconnected stages. In 

 a transverse section a little above the one figured (PI. xiii, Fig. 14), 

 the stomatodaeum is seen to lie in close apposition to the column 

 wall, there being no endoderm between its mesogloea and that 

 of the column. A little lower, as in the section figured, it has 

 separated, and the mesentery is to be seen extending from it to 

 the column. The axis of the stomatodaeum is oblique to the 

 long axis of the embryo, and therefore the section does not cut 

 the stomatodaeum transversely. The other mesentery of the 

 first pair is seen also in this section, and it is noticeable that it 

 has made its appearance independently of any apposition of the 

 stomatodaeum to its point of origin. In another specimen 

 (Fig. 15), however, I find that such an apposition does occur 

 in the manner described by H. V. Wilson for Manicina ('88), 

 the stomatodaeum passing over from the point of origin of the 

 first formed mesentery, drawing this with it, to apply itself to 

 the column wall at the region where the second mesentery is to 

 be formed. It is certain, however, that this apposition of the 

 stomatodaeum is not necessary for the formation of the second 

 mesentery, which may rise while the stomatodaeum is still in its 

 upper part in contact with the place of origin of the first mes- 

 entery. 



There is as yet no development of mesenterial filaments. 

 The stomatodaeal ectoderm can be traced downwards in a series 

 of transverse sections somewhat further on one side than on the 

 other, but this is a necessary consequence of the obliquity of 

 the stomatodaeum to the long axis of the embryo. It is possible 

 that there may be a slight elongation, but it is doubtful, since 

 in the specimen from which Fig. 14 is taken, the stomatodaeal 

 ectoderm is cut in the sections lower down on the side on which 

 the stomatodaeum is in contact with the column wall than on 

 the other, and if we consider this as indicating the formation of 

 a filament, we will have the filament of the second mesentery 

 more fully developed than that of the first, which is possible, 

 but not to be expected. 



The stomatodaeum is now slung by two mesenteries. It lies 



