THE DEVELOPMENT OP ASTEEINA GIBBOSA. 273 



a pr8eoral sense-organ is present ; this subsequently becomes 

 incorporated with the ciliated ring, and if this organ is homo- 

 logous with that of the Bipinnaria, we may conclude that the 

 ciliated band of the Pluteus corresponds only to the posterior 

 of the two bauds of the Bipinnaria^ since in the Bipinnaria 

 the sense-organ is situated between preeoral and post-oral 

 ciliated bands, and this spot corresponds to a constriction in 

 the original longitudinal ciliated ring, not to a position on its 

 anterior edge. 



Our knowledge of Echinoderm histology is largely due to 

 Hamann (8) and Cuenot (3 and 4). The latter, as we have 

 seen above, was the first to suggest that the ovoid gland gave 

 rise to the genital rachis. The first account of the development 

 of ovoid gland and rachis is given in my paper on Amphiura 

 squamata (14), and I have there collected the fragmentary 

 notices on this subject, which had till then appeared. 



[I regret that when I sent in this paper for publication I did 

 not mention the well-known paper of MetschnikoiF (" Studien 

 liber die Entwickelung der Echinodermen und Nemertinen,^' 

 ' Memoires de I'Academie Imperiale de St. Petersbourg,' tome 

 xiv, No. 8), in which he describes a right hydroccele in 

 Amphiuria squamata. He there says that the right ccelomic 

 vesicle becomes divided into anterior and posterior portions 

 just like the left; the anterior portion sometimes atrophies but 

 sometimes develops into a regular five-lobed hydroccele. It 

 has been the fashion to ignore this work, since it was not 

 accomplished by modern methods; but after my experience 

 with Asterina I feel morally certain that Metschnikoff was 

 right, though of course he did not distinguish between 

 hydrocoeles and anterior ccelom. Bury (3) seems to have missed 

 the importance of this observation. — Dec, 1895.] 



General Considerations. 



On reviewing the developmental history recorded in this 



paper, two main questions present themselves : first, what 



light does it throw on the affinities of the Asterids with other 



Echinoderms? and second, does it suggest any direction in 



