ON DEVELOPMENT ETC. OF PHOllOXIS. Ö09 



Before proceeding further, I beg to tender my sincere thanks 

 to Professors Mitsukuki and Ijima for their kind supervision 

 of my Avork and for their ])aiiistaking revision of my manuscripts. 



Contents. 



I. The Eurly Development uf the l*liuruiii,s ]jarva. 



((. Xotes on Fertilization. 



b. Notes on Segmentation. 



c. Gastrulatiou and Mesohlast-Formatiou. 



(1. Further Observations on the Development of the Lirva. \\\) to 

 tlie Period when it becomes free-swimming. 



II. The Structure of Actinotrocha. 



a. The External Appearance of Actinotroclui. 

 h. The Internal Structure of Actinotrocha. 



1. Body-Divisions and Body-Cavities. 



2. Organs of Ectoblastic Origin, 



3. Organs of EntoLlastic Origin. 



4. Organs of Mesoblastic Origin. 



III. Metamorphosis. 



IV. Supplementary Notes. 



I. The Early Development of the Phoronis Larva. 

 a. Notes on Fertilization. 



Phoronis is, as is well known, a hermaphrodite, in which hotJt 

 iliG mah and female sexual elements mature at nearhj the same 

 time. Put few authors seem to have studied tJu> animal duriug its 

 breeding season, so that our knowledge of its sexual organs and, 

 consequently, of its fertilization has remained very imperfect, as 

 was pointed out l)y Cora ('91). The only existing statement as 

 to how and wliere fertilization is accomplished in Phoronis is that 

 of Kow'ALEAVSKY ('07). Tlus author thought that fertibzation 



