No. 2.] DEVELOPMENT OF MARINE ANNELIDS. 257 



Wilson holds for Nereis} I see no conclusive evidence, for or 

 against this supposition. 



The ventral cord is differentiated as usual from the ectoderm 

 of the ventral plate. Ganglia, connectives, etc., are formed 

 while the larva is still in possession of prototroch and paratroch, 

 and the first ventral ganglion lies in the first setigerous segment. 



Fig. X. — Trochophore of Amphitrite, 

 about 20 hours; ap.tft., apical tuft; 

 prot., prototroch; par., paratroch. 



Fig. XI. — Amphitrite, 24 hours, ventral 

 aspect; ap.tft., apical tuft; prob., prob- 

 lematic bodies; gl., duct of umbrellar 

 mucous gland; tmic, subumbrellar mu- 

 cous gland; par., paratroch; prot., pro- 

 totroch. 



Proble7natic bodies. — At about the time the anterior mucous 

 glands begin to react to the methyl-green, there appear in the 

 ectoderm near the openings of the glands five spherical bodies, 

 disposed symmetrically, one on the mid-ventral line, two on 

 the ventral, and two on the dorsal side. They increase rapidly 

 in size up to a certain point, and remain as long as the mucous 

 glands and the prototroch. They appear to be spherical vesicles 

 filled with a fluid, which does not react to methyl-green nor 

 Delafield's haematoxylin like the substance of the mucous 



