DEVKLOPMEXT, STRUCTURE, ETC., OF ACTINOTROCHA. 485 



Review of Mr. Iwaji Ikeda's Observations on 

 the Development, Structure, and Metamor- 

 phosis of Actinotrocha.^ 



By 



A. J. Mastcriuaii, 



Edinburgh. 



Zoologists are indebted to this publication of the Tokyo 

 University for an account of many valuable zoological re- 

 searches, and by no means the least important is contained 

 in the volume now lying before us. Mr. Ikeda has been 

 enabled to study the living larva and the embryonic stages 

 at the Misaki marine station. The newly described species, 

 Phoronis ijimai, Oka, furnished the embryonic stages, and 

 for the structure of the larva no less than four species (?) 

 were examined. Of these perhaps the most remarkable is 

 type D, which is a large larva about 5 mm. in length and 

 with about forty-eight tentacles. 



In the embryonic development we naturally look at the 

 parts dealing with such a much-disputed point as the origin 

 of the mesoblast. Anyone who has studied the literature of 

 the development of Phoronis will be able to gather a clear 

 account of the general features, and will be led to conclude 

 that the minor differences between the various Avorkers are 

 largely specific. Speaking generally, a total equal segmenta- 

 tion, producing a blastula larva, invagination to form a 

 gastrula, and the persistence of the blastopore as the larval 



^ 'Journal of the College of Science,' Imperial University, Tokyo, Japan, 

 vol. xiii, pt. 4, 1901. 



VOL. 45, PART 3. — NEW SERIES. K K 



