PROCEEDINGS 



ROYAL SOCIETY OF EDINBURGH. 



VOL. II. 1846-7. No. 30. 



SixTY-TniRD Session. 



Seventh Ordinary Meeting, \st March 1847. 



Sir THOMAS MAKDOUGALL BRISBANE, Bart., 

 President, in the Chair. 



The following Commiihications were read : — 



1. On the co-existence of Ovigerons Capsules and Spermato- 

 zoa in the same individuals of the Hydra viridis. By 

 Dr Allen Thomson. 



In this communication, the author described some observations 

 made by hira in the autumn of 1845, by which he had ascertained 

 that in the Common Green Polype, as had previously been observed 

 in the Hydra fusca, generation takes place at the approach of winter 

 by the development of impregnated ova. 



Professor Thomson ascertained, that, at this season, while a num- 

 ber of the polypes bore the spermatic capsules near the base of the 

 arms, a few animals were to seen, on which, besides these capsules, 

 an ovum was developed from the exterior of the middle of the body. 



The act of fecundation was observed : the sub-division of the yolk, 

 while the ovum stUl remained in its capsule, attached to the parent, 

 was distinguished, as well as the subsequent separation of the ovum ; 

 but the author had not an opportunity of tracing the formation of a 

 young polype from the ovum. 



VOL. II. M 



