376 ARTHUR T. MAS'l'EUMAN. 



oral, and vice versa. The eggs after deposition measured 

 ^i^ incli in diameter. 



Kowalevski (9) in 1867 published the results of his labours 

 upon Ph or on is at Naples. Some observations upon the 

 anatomy are followed by an account of the early develop- 

 ment. He states that fertilisation takes place in the coelom. 

 Total cleavage leads to the formation of a hollow sphere, 

 which invaginates. The mesoderm is formed by delamina- 

 tion from the ectoderm. The blastopore shifts from a ter- 

 minal to a ventral position. Further development results 

 in the formation of the hood over the mouth and the ten- 

 tacles at the posterior end. Between the latter the anus 

 breaks through. On becoming set free from the egg 

 membrane the larva is uniformly clothed with cilia. He 

 succeeded in definitely identifying the Phoronis larva as 

 being none other than Actinotrocha. Finally, he was led 

 to consider that Phoronis had no connection with the 

 Grephyrea or the Bryozoa. In fact, he doubted the cor- 

 rectness of placing it amongst the worms, himself inclining 

 rather towards the Mollusca as its true phylum. 



Metschnikoff (13) in 1871 gave an account of early Ac- 

 tinotrocha larv£e and their structure in so far as could be 

 ascertained from external observation. He figures and 

 describes a free-swimming larva with one pair of tentacles, 

 and follows this up through stages with two and three pairs 

 of tentacles. His description of stages later than tliis do not 

 concern the present subject. 



In 1882, however, in a paper (14) dealing generally with 

 gastrulation and the origin of the mesoderm in Metazoa, 

 he follows these processes in Phoronis from the blastula 

 onwards. He appears to have relied solely upon an exami- 

 nation of the entire embryos for his results. He shows large 

 mesenchyme cells present in the blastocoele cavity before 

 gastrulation, and smaller ones scattered during this process 

 in the reduced cavity, more especially in the pre-oral lobe. 

 In this region they are figured as arranging themselves as a 

 layer lining the cavity. From these observations he is led 



