212 TORREY 



in Ecliiiirus a lack of food and poor environment seem to in- 

 crease the amount of pigment and decrease the number of S- 

 shaped glands. In Thalasseina, I believe, the differences are 

 due merely to individual variations and are quite independent 

 of the presence or absence of food, for the variations appear 

 before the animals have begun to take in nutriment. Spengel 

 ('97) figures an abundance of green pigment in the larva of 

 Bonellia. A very careful search was made for ectodermal mus- 

 cles, which, according to both Hatschek and Conn, lie in the 

 body wall. I think that it may be stated, with absolute cer- 

 tainty, that no such muscles are present in the trochophore of 

 TJialassema. The wrinkles in the outer cuticle simulate quite 

 closely muscle fibers and might easily have been mistaken for 

 them. 



b. Ciliation, — The fact that the prae-trochal region is pro- 

 vided with scattered patches of cilia (Text- Fig. 8, A) seems to 

 be in accordance with the widely accepted theory that at an 

 earlier stage of its evolution the trochophore was entirely cov- 

 ered with cilia, as is the case to-day in the young Pilidiuni larva 

 and the young trochophores of Teredo, Dentaliiim, Nucida, 

 Yoldia and ChcEtopterus. In most forms, however, the cilia 

 have become restricted to certain definite regions. The para- 

 troch in Thalassemia appears very late, after 36 hours, and is 

 formed without doubt from cells of the somatic plate which 

 were originally in close proximity to the prototroch. These 

 cells, it will be observed, are different from those which enter 

 into the formation of the paratroch \n A i?tphitr it e diwd Arenicola. 



The oesophagus develops strong cilia even before its complete 

 differentiation. At the opening of the oesophagus into the 

 stomach a circle of long cilia hang down into the latter (see 

 Text-Fig. 8, A). The stomach wall, itself, is covered uni- 

 formly with fine cilia, but these seem later to be restricted to 

 certain swollen regions presently to be described. The wall of 

 the intestine is also ciliated. A very curious ciliated groove or 

 ridge (it was impossible to determine with certainty which) runs 

 from the stomach into the intestine, a little to the right of the 

 ventral side. At its stomach end it is bent in a half spiral and 



