THF BODY-CAVITIES OF TUR STAR- F FSH. 



81 



larva in an intermediate stage between stages C and D of MacBridf, proves the 



same fact still more conclusively. Here one 



sees the primary mesentery dividing the left 



a posterior from the right posterior enteroccel 



still persisting but considerably thinned out, 



while at a short distance from it on the right 



ß side there has been formed a second septum 



by the apposition of the peritoneal walls. 



a epigastric enteroccel, 6 portion The primary mesentery subsequently ruptures 

 of the right posterior enterocrel cut 



off from the rest, c left posterior an( \ leaves no trace, while the secondary sep- 

 enter ;cœl. 



tum is gradually completed and finally be- 

 comes a true mesentery by ingrowth of the mesenchyme and the consequent 

 separation of the two secondarily formed cavities. The one lying entirely on the 

 right side is the epigastric enteroccel, and the other lying mostly on the left side 

 and extending on to the ventral side is the secondary left posterior enteroccel. It 

 is evident from what has been said that the latter is equal to the left posterior 

 enteroccel of the larva plus about one-half of the right posterior enteroccel of the 

 same. This is also true of Anterias pallida. 



The circular enteroccel and a portion of the perihsemal system arise in 

 Antenna giìòosa in a very different way from what takes place in Asterias pallida. 

 According to MacBride the entire perihsemal system of authors, viz. the circular 

 enteroccel plus the perihsemal system of the present writer, arises in the form of 

 five interradial out-pocketings of the secondary left posterior enteroccel. Accord- 

 ing to my observations there are only four interradial out-pocketings from the 

 secondary left posterior enteroccel, viz. in interradii 4-5, 2-3, 3-4, and 5-1. ¥ In 

 interradius 1-2 the out-pocketing is replaced by the axial sinus (anterior entero- 

 ccel). The four out-pocketings, after being completely divided off' from the 

 secondary left posterior enteroccel, grow towards, and unite with, each other and 

 with the axial sinus, and forms a complete ring. This ring is subsequently divid- 

 ed into two concentric portions by the formation of a septum ; these are the two 

 perihsemal ring-spaces of authors. Before the formation of this secondary septum, 

 however, the peripheral portions of the four out-pocketings and the oral portion 



* Adopting Mac-Bride's notations. 



