

The Organogeny o/Asterina gibbosa. 431 



December 7, 1893. 

 The LORD KELVIN, D.C.L., LL.D., President, in the Chair. 



A List of the, Presents received was laid on the table, and thanks 

 ordered for them. 



The President announced that he had appointed as Vice-Presi- 

 dents 



The Treasurer. 



Sir John Lubbock. 



Dr. Per kin. 



The Marquis of Salisbury. 



The following Papers were read : 



I. " The Organogeny of Asterina gibbosa'' By E. W. MACBRIDE, 

 B.A., Demonstrator of Animal Morphology to the Uni- 

 versity of Cambridge. Communicated by ADAM SEDGWICK, 

 F.R.S, Received September 13, 1893. 



Having been engaged in studying the development of Asterina 

 gibbosa during the past year, I think it advisable to publish an 

 account of the results already obtained, as these are of considerable 

 interest, and it may be long before I can complete my investigation. 

 As this is only a preliminary account, I shall ignore statements 

 which conflict with my results, noticing only the results of other 

 workers in so far as they confirm my work. 



The classic research of Ludwig* on this subject is well known. 

 The advances I have been able to make on his work concern chiefly 

 the later larval stages and the metamorphosis. 



Ludwig finds a regular segmentation, giving rise to a ciliated 

 blastula ; typical embolic invagination follows, and the blastopore, 

 placed at first in the centre of the ventral surface, is carried by 

 growth to near the posterior end, and functions for a short time as 

 larval anus. In the meantime the archenteron becomes divided into 

 an anterior thin-walled portion, and a posterior thick-walled one. 

 The latter becomes separated as the definitive gut, which is soon 

 joined by the larval oesophagus, which arises as an ectodermic invagin- 

 ation, the former becomes the ccelom, sending back a horn on each side 

 of the gut. On the left side, in the praeoral portion of the ccelom, we 

 find a pore opening to the exterior the madreporic pore. 



* " Entwickhmgsgeschichte der Asterina gibbosa." c Zeitschrift fur Wiss. 

 Zoologie,' yol. 37. 



VOL. L1V. 2 H 



