DEVELOPMENT, STRUCTURE, ETC., OF ACTINOTROCHA. 487 



of their presence, e. g. his fig-. 33. Perhaps I may add that 

 in P. hippocrepia I have found certain mesenchymatous 

 cells at the gastrula stage, and I think it is possible to regard 

 these as having the same relation to the mesoblast arising 

 from the invaginated hypoblast as similar mesenchymatous 

 cells have to the enterocoelic mesoblast of Echinodermata. 



From this it will be clear that it is not difficult to gather a 

 fairly consistent account of the origin of the mesoblast from 

 the figures of Caldwell, Ikeda, and myself. 



But the second part of Ikeda's memoir, dealing with the 

 larval structure of Actinotrocha, is unquestionably the most 

 important and the most welcome at the present time. Since 

 my paper on this subject in this .Journal Professor Eoule 

 has, at international congresses, in the ' Zoologische Anzeiger,' 

 and in several French journals (^ Comptes rendus,' 'Annales 

 des Sciences naturelles,' etc.), spared no pains in reiterating 

 that the essential facts as described by me, such as the 

 presence of coelomic cavities, mesenteries, and so on, which 

 led me to regard Actinotrocha as a highly organised 

 coelomate larva, were mere figments of imagination, or were 

 due to this factor combined with a judicious admixture of 

 defective technique. On the other hand, he has insisted 

 that it is to be regarded as at the morphological level of 

 the trochophore. No one comparing our figures could possiblv 

 reconcile the two series of results. Roule was perfectly right 

 in saying that if "his descriptions are accurate mine must 

 be untrue, and we are perfectly justified in believing the 

 converse. It is therefore, from the point of view of 

 zoological progress, eminently satisfactory that my work has 

 received so complete a corroboration as the present. 

 Speaking candidly, we do not think that the author has 

 fully appreciated, or at least emphasised, the corroborative 

 nature of his work. With one or two important exceptions, 

 to be noted later, the whole of his anatomical drawings might 

 be used as they stand to illustrate my paper of 1897. We 

 can read through page after page of his description in 

 which the anatomical details are a virtual repetition 



