104 EDWIN S. nOODRICH. 



Few new points are presented in this paper, the work 

 having been chiefly of a critical and corroborative nature ; 

 but the results of the study of this interesting larva which 

 have been published are so contradictory that no apology 

 need be made for an attempt to I'econcile such conflicting 

 views. 



Although the larva of Phoronis was discovered and de- 

 scribed b}^ Johannes Miiller as early as 184G, and several 

 zoologists have studied it since, many points in its anatomy 

 and development remain still but imperfectly known. 



The literature on the subject has been so well and so 

 recently analysed by Masterman (11), de Selys Longchamps 

 (16), and Ikeda (9), that it is only necessary for me to refer 

 to those writings of previous authors which deal more parti- 

 cularly with the body-cavities and nephridia.^ 



The earlier observers gained a good general knowledge of 

 the external features of various stages, of the chief events in 

 the metamorphosis, and of the general internal anatomy of 

 Actinotrocha (Miiller [15], Wagener [18], Krohn [10], 

 Schneider [17], Claparede [4], Metschnikoff [14], Clegenbaur 

 [5]). But to Caldwell belongs the credit of first presenting, 

 in 1882 (2), a clear account of the details of the internal 

 anatomy and of the internal changes undergone during meta- 

 morphosis. Unfortunately Caldwell's paper was not accom- 

 panied by adequate figures. Nevertheless his observations 

 were so accurate and so detailed, and his interpretation of 

 the morphology of the larva was in the main so good, that his 

 successors have done little but corroborate, extend, and, in 

 some respects, correct his results. 



The Cavities. 



According to Caldwell (2) there are in the Actinotrocha 

 larva two main cavities, separated by a complete septum ; 



' Roule's results differ so fundamentally from those of otlier writers and 

 from my own that it seems safer not to criticise his work without having 

 studied Iho species he examined ('Ann. des Sci. Zoologie,' vol. xi, 1900). 



