WYVILLE THOMSON, OX SYNAPTA INHiERENS. 143 



They nearly doubled in size, lost tlieir ciliated bauds, and 

 became vermiform. As in Synapta, rapid peristaltic expan- 

 sions and contractions passed along the body. At this stage 

 the movith opens into a short oesophagus, which is inserted 

 into the wider stomach, with a slight inflexion. The in- 

 testine is suspended in the cavity of the body by a plexus 

 of delicate muscular cords, which seem to have a share 

 in producing the perpetual expansions and contractions 

 to M'hich this organ is subjected. The anus is in the axis of 

 the body, and terminal. Two pulsating vessels pass along 

 the surface of the intestine, from the oesophageal extremity. 

 One of these, the wider, lies close along nearly the entire 

 length of the intestine, loosens itself from it during its 

 course, and continues free to the anus. From this free 

 portion a short cross branch passes to the intestine. 



Eleven days after capture no essential change could be 

 detected in the *^' Kalksack^^ or dorsal canal, and the pore of 

 the dorsal canal seemed not yet obliterated. Dr. Krohn had, 

 in one case, an opportunity of observing the development of 

 three new tentacles. They originated in csecal processes from 

 the circular canal of the ambulacral system, close to the pairs 

 of vesicles, with tremulous double nuclei. They gradually 

 increased in length, till they reached the membrane, w^hich 

 forms a duplicature between the bases of the originally 

 formed tentacles. They penetrated between the two walls of 

 this duplicature, and, at length, reached the free border. 

 Though still much smaller than the primitive tentacles, they 

 had all their characteristic structure. Dr. Krohn was unable 

 to pursue their development further. 



On the 9th of March, 1852, Messrs. Danielssen and Koren 

 ("Bidrag til Holothuriernes Udviklingshistorie," 'Fauna 

 littoralis Norvegise.^ Second part, Bergen, 1856), observed 

 certain minute spherical bodies floating on the surface of the 

 water in Bergen bay. Tinder the microscope these bodies 

 proved to be eggs undergoing segmentation, embryos rotating 

 within the vitelline membrane, and free embryos. The 

 embiyos were oval, were entirely covered with cilia, and pre- 

 sented a slight depression at the anterior extremity. Two 

 days later the embryos were more pyriform, a buccal orifice 

 had been formed at the bottom of the anterior depression, and 

 a distinct digestive cavity was observed containing moving 

 granules. The external wall was soft, homogeneous, and 

 finely granular. Five days later the margin of the body 

 seemed thrown into undulations. The external wall was 

 slightly opaque, and on the dorsal surface, at some distance 



