66 CONKLIN — EMBRYOLOGY OF A BRACHIOPOD. [April 4, 



however are so important and extend to such details that I am 

 inclined to accept the view that Phoronis and the Brachiopoda are 

 related, and to look to future work on the development of both of 

 these groups to harmonize the apparent differences between them. 



(c) Comparison with Larval Folyzoa, 



Brooks in particular has emphasized the resemblance between the 

 larvae of Polyzoa and Brachiopoda, basing this comparison, how- 

 ever, rather upon the external characters in which both resemble 

 the trochophore than upon a detailed comparison of internal 

 structure. 



Ectoprocta. — It is extremely difficult to compare larval brachio- 

 pods with larval ectoprocts, owing to the great variety of forms 

 presented by the latter, their many secondary characters, and the 

 conflicting accounts of their structures and homologies which have 

 been given by various authors. There is some reason for believing 

 however that the ectoproct larva belongs to the trochophore type, 

 and that the following parts of the two may be homologous: (i) 

 The retractile disk may correspond (at least in part) to the apical 

 plate, (2) the corona in part to the trochus, (3) the sucker to 

 the trunk of the trochophore, or to the ventral evagination of 

 Actinotrocha. Furthermore one may trace a certain resemblance 

 between the invaginated sucker of Bugula and Lepralia and the 

 peduncle and mantle of Terebrafidiiia. In both cases attachment 

 takes place by the peduncle, while the covering folds (mantle in the 

 case of brachiopods) are turned forward as the peduncle is protruded. 

 However the degeneration and modification of structures, both in 

 the larval stages and in the metamorphosis, are so extreme that any 

 attempt at the present time to trace homologies between larval 

 Ectoprocta and other forms must be accompanied by a lively 

 imagination and a ready facility in guessing. 



There is good evidence in the degeneration of the intestine and 

 coelom of the ectoproct larva, and in the general degeneration 

 which accompanies its metamorphosis, that we are dealing with a 

 highly modified type of development, which is little likely to throw 

 light upon the affinities of the Polyzoa. However the resemblances 

 between the adult Polyzoa and Phoronis and the Brachiopoda is 

 such as to warrant the conclusion that these groups are at least 

 remotely related to one another. 



Enfoprocta. — Among larval entoprocts there are few, if any, 

 undoubted homologies with either the trochophore, the actinotroch, 



