DEVELOPMENT, STRUOTQUE, ETC., OF AOTINOTROCHA. 491 



important verifications of the results of his predecessors^ and 

 the few differences from my work which I have indicated 

 above, he has also added several interesting and new facts. 

 He describes two retractor muscles of the hood which run 

 from the main nerve-ganglion down to the dorsal body-wall. 

 In one larva he finds a pair of long trunk-retractors. We 

 may also note the description of a pair of globular glands 

 which open on the dorsal wall of the hood in one species of 

 larvae, but not in the others. 



In the third part of his paper the author deals with the 

 metamorphosis. As one who has attempted many times to 

 follow in detail this important process, and each time has 

 been forced to wait for more material, I can speak of his 

 attempt with sympathy. At the same time it will be well to 

 accept with great caution all results, especially referring to 

 the mesodermic organs. The external changes have already 

 been carefully noted by many, and the changes of the 

 alimentary canal are also easy to follow. In describing 

 these latter we may note that Ikeda is able to correct the 

 obvious error of Roule that the intestine ruptures, and that a 

 fresh intestine is created from the cordon dorsal. (As is 

 to be expected, he finds that this organ is the dorsal blood- 

 vessel.) But when we come to the mesoblastic organs the 

 difficulties begin. According to Ikeda, an "adult" collar 

 cavity (or the supra-septal cavity) is formed round the base 

 of the tentacles apparently from part of the larval collar 

 cavity (at least the walls), and the rest of the larval cavity is 

 converted into the blood ring-sinus of the adult. The diffi- 

 culties relating to the nephridial openings into the trunk, 

 the adult nervous system, and the epistome are discussed, 

 but one would desire the author to pursue his studies on the 

 metamorphosis, and it is pretty certain he will find that 

 arguments from probabilities have no weight whatever with 

 a metamorphosing Phoronis. At least, this is the writer's 

 experience, and it is the main reason which conduces to a 

 belief in the fate of the larval collar cavity as described by 

 the author. But these remarks are not in any way meant to 



