66 



there is an opening between the zocEcium and the ooeciuni in the separating wail, 

 but I must disjjute its presence, as I liave always by transverse grinding found 

 the separating wall unlirolvcn. Calvet has found an ooecial operculum with two 

 layers, which is opened Ijy a muscular apparatus. 



5) The double-valved ooecia (PI. VII, figs. 3 a, 3 h, 3 i, 3 j, 3 k, 3 I) which 

 have hitherto only been found in Aliisidiiim ixtrasiticnin, consist of two double 

 layered, arched valves, the edges of which meet together and with the zooL-ciuni 

 bearing them form a bean-shaped body. They rise from zott'cia, Ibe oral surfaces 

 (PI. VII, 3 c) of which form nearly a right angle with the longitudinal axis of 

 the zoircium, and the two valves arise in the lateral borilers of the said surface 

 on each side of the zooccial aperture, which leads directly into the bottom of the 

 ooecium. As each of the two hollow valves has an inner connection with the 

 zocecium through a pore-chamber, we must regard them as two kenozooecia (see 

 under Ahisidiuiu pardsiticiiiu). 



()) The acanthostegous ooecia. We indicate by this name the cavities found 

 in the two Elvctia species, E. zostericohi (PI. IX, fig. 2 b) and E. (Hctenvcium) 

 amplectens (PI. IX, figs. 1 a, 1 c), which externally are limited by two lows of 

 hollow spines meeting together in the middle line of the frontal surface. The 

 od'cial cavity in E. zostericola is bounded internally by tlie frontal membrane of 

 the zou'cium, and externally by the mentioned spines, and according to Ostrou- 

 moff this cavity contains developing larvae. While the zooecial operculum in 

 the species mentioned is placed at the distal end of the ooecium-bearing zoa^cium, 

 in the corresponding zoacia of E. amplectens it is situated proximally to the 

 area formed by spines, and as this species has only been examined in dried 

 condition, nothing is known as to how far the ocBcial cavity also here is bounded 

 in tlie same way as in E. zostericola. 



Before leaving this subject, we may briefly touch upon the question of the 

 egg's transference into the oircium. The older view that the egg is carried from 

 the zoa-cium (or gonozo(i'cium) into the oaxium througli an inner connection 

 seems according to Jullien's investigations to hold good for Hippolhoa hijalina, 

 in which sj)ecies the gonozooecium and the orecium form a common cavity, 

 closed by a common operculum. According to Jul lien- the zoa>cium has no 

 polypide but contains an ovary, and he supposes that the tentacular sheath is of 

 service to the egg by carrying it over into the ocpcium. A similar direct trans- 

 ference probably occurs also in all the cases where endoocecial ooecia are present 

 with an operculum in common with the zoa-cium (llippotlioidac, ('.iilrniiriulnc. etc.). 



' 90, p. 19. '' 4,5. p. 31. 



