266 



McMURRICH. 



[Vol. II. 



the first formed (I), and the two smaller are those indicated in a 

 previous paper ('9ia, PI. IX, Fig. 6), as Vand VI. 



The larger mesenteries, when traced upwards, are seen to 

 become attached to the stomatodaeum, while the smaller ones 

 are imperfect. The epithelium which represents the glandular 

 streak seems to be continuous above with the ectoderm of the 

 stomatodaeum in the cases of the perfect mesenteries, though 

 close examination shows some slight differences in the two 

 epithelia. In the cases of the imperfect mesenteries such a 

 continuity is out of the question, and there is not the slightest 

 indication of a band of ectoderm extending up the outer wall 



of the stomatodaeum, across 

 the under surface of the disc 

 and thence down the free 

 V edge of the mesentery, by 

 which a connection between 

 the glandular streak and the 

 stomatodaeum might be ac- 

 complished. The glandular 

 streak epithelium can be 

 traced upwards upon the im- 

 perfect mesenteries to a level 

 a little above the lower edge 

 of the stomatodaeum, where 

 it fades out, the free edges of 

 the mesenteries being occu- 

 pied from that point upwards 

 by cells of exactly the same nature as those covering their sur- 

 faces. That there may have been in an earlier stage some con- 

 tinuity between the stomatodaeal ectoderm and the glandular 

 streaks of the imperfect mesenteries is possible ; in my youngest 

 embryos there are, however, no signs of any such connection. 



In the adult condition mesenteries V and VI have no fila- 

 ments (VI has in macrocnemic forms), and one might expect 

 that older embryos would show a disappearance or diminution 

 of the filaments of those mesenteries. In Fig. 1 1 is represented 

 a part of a section through an older larva, in which the number 

 of the mesenteries still remains at twelve. The filaments, how- 



Fig, lo. — ■ Transverse section through a portion 

 of the column of a young zoanthid larva. 



