(IV) 



"Po nnat i o i^ o f _ 1 1 . e_ Me s o cl e r m, 



There is coiisiuorable ai+'ferei.ce of opinioii amoJiL; those 

 wiio nave iiivestit^atea the einbryolot^y of Ph.)roiiit; as to ti.e ori- 

 gin of the mesoderm aiid there seem to be iiO two v/iiose ucacrip- 

 tioiid atiree^altr.outh Ikecta (9) ana Loiii^cuixmi,s (1^) in their re- 

 ceiit papers ai-ri ve at tiie sarue coiicliisioviS , {^jue rally apeak-int^. 



I cLtu cciiViiiced froi:! ncj ov/u dti:ay o f the e^^^^s ana larvae 

 of Phoronis architecta ana tnoso uf Phoronio Auat'-cilis that the 

 great ai "Inference in the orit^in of tr.e aiesoaerni as Roule {kO} 

 and Masterman (16) see it, is auc, in a gi^eat part, to dif-f'er- 

 ence in the larvae t heiaselvos, 



Tne eg^vs and embryos o *' Phoronis Australia, for 'vi.ich I 

 siri a^vcn inaebted to Mr. Ikeda, are vc ^^y similar in appeara^^ce 

 to those of Phoronis Euskii, jutii-Ziiii^ from Masterman's fi<2;ures 

 (16). Sections o ^' the e^^us and larvae of the former show the 

 aevelopment to be of tne same i:,Ciieral type as that of' Phoronis 

 Ijimsd "'iiicn Ikeda (9) r.as aescribea. 



The etjC^ ana larvae of Phoronis arcnitecta are consiacr- 

 ably different from those ms.ntioned above. They are more re^^- 

 ular in form, the blastocoel is much mo ro spacious cina tne cell? 

 ti.emsnlves are more re^^Tilar in shape and arraij^cmont . Tuey are 

 most simixo,'- in appearance to the early sta^^es o " Phoronis 3a- 



