ASTERIAS PALLIDA. 263 



brachiolar ann.s are still very distinct. In Fio-. 18 is given a series of 

 frontal sections of the specimen represented entire in Fif>\ 18*, beo-innino- 

 from the ventral side ; so tliat it is directlv comparable with Fig. 17? 

 which is taken from stage D. 



Together Avith the aboral disc the epigastric enterocœl has assum- 

 ed its definitive position and Hes directly under the central portion of 

 tlie f)rmer. It sends out diverticula, into the arms of the star, which 

 althougli distinct are yet short and blimt. In Fig. LS a, h, and t] one 

 sees these diverticula in transverse sections. The whole cavity is con- 

 fined to the aboral side, and is even here encroached on more or less 

 by tlie secondary left posterior enterocœl, as is clearly seen in Fig 18. 

 This condition of the epigastric enterocœl persists, with a slight modifi- 

 cation, to tlie adult stage. 



The secondtiry left posterior enterocœl has been almost wholly cut 

 off f'njm the anterior enterocœl on the right side, by the form:iti(jn of a 

 septum from its walls at the boundary line ])etween the anterior and 

 posterior enterocœls. The coincidence in position of this imaginary 

 boundary line and the septum just mentioned is so exact th:it I do not 

 hesitate in affirming tliat this secondary separation takes place exactly 

 at the place mentioned. The septiun is in stage F still incomplete, as 

 may be seen in Fig. 18 c, where the two cavities communicate with each 

 other on the right side. The secondary left .posteri<jr enterocœl has 

 uow tlie form of a ring incomplete at one point, viz., on the dorsal 

 median line, where the two portions are permanently separated from 

 each other. It also sends out diverticula into the arms. 



If the descri])tions and their interpretations detailed above are 

 correct, then the following equations must liold : 



* The shriakage, which is considerable, is due solely to the usual treatiiieat to which an 

 object is subjected foi- iui bedding- in paraffin. 



