ON THE DEYELOPMENT OP THE OTENOPHOEA. 89 



Anniteesart Addeess oe THE Peesident, 

 Professor Allman, M.D., LL.D., F.E.S. 



Becent Progress in our Knowledge of the Development 

 of the Ctenophora. 



[Eead May 24, 1881.] 



In accordance with my usual practice of making the Anuiversary 

 Address of the Linnean Society an exponent of recent progress 

 in some department of zoological research, I have selected for the 

 present occasion the additions which have of late years been made 

 to our knowledge of the development of the Ctenophora. 



In the summer of 1861 Beroe ovata made its appearance in 

 great numbers in the Firth of Forth, and afforded me an oppor- 

 tunity of subjecting this beautiful Ctenophore to a careful ana- 

 tomical and embryological study, and of making numerous draw- 

 ings illustrative of its structure and development. Before, how- 

 ever, all the points I had wished to ascertain had been made out, 

 the animals had disappeared from the coast ; and in the hope of 

 obtaining at a future period fresh subjects for examination, I con- 

 tented myself with publishing an abstract without figures of the 

 facts which I deemed most important, deferring the publication 

 of the more detailed memoir to such time as I might be enabled 

 to complete the unfinished observations. The opportunity, how- 

 ever, of doing so never occurred. 



In this abstract * I called attention to the existence in the egg 

 of an external structureless membrane, which is separated from 

 the vitellus by a clear interval, while the vitellus itself previous 

 to segmentation shows a differentiation into a denser peripheral 

 layer and a central portion, which has the appearance of being 

 composed of cells with clearer contents. The later observations 

 of Chun go to show that this semblance to cells is only the ex- 

 pression of a vacuolated condition of the vitellus. 



I pointed out that while the first stages of segmentation pro- 

 ceed in the usual way, the segmentation in its subsequent stages 

 joes not go on uniformly in all the previously formed cleavage- 



* ' ' Contributions to our Knowledge of the Structure and Development of the 

 Beroidro," Proc. Eoy. Soc. Edinb. vol. It. p. 619 (1862). 

 LINN. JOTJEN. — ZOOLO GY, VOL. XYI. 7 



