|[48 John H. (jebould. 



The distinctive features of Sipnncuhis may be briefly summarized 

 as follows: a tentacular fold is present, without isolated tentacles; 

 a median-dorsal unpaired epithelial tube in the adult opens upon 

 the surface, immediately behind the tentacular fold, and leads back- 

 ward to a cerebral sense organ, which is situated anterior and 

 ventral to the brain; bicellular glands occur in the skin, but no 

 hooks are found in the integument of the introvert'. The prototroch 

 cells of the embryo become modified into an embryonal envelop, 

 which is cast off with the vitelline membrane. 



Phascolosoma has numerous flattened, isolated, finger-shaped 

 tentacles, a ciliated sense organ (nuchal organ), situated on the 

 surface immediately dorsal to the circlet of tentacles, and probably 

 homologous to the cerebral organ of Sipimcnhis, a pair of tubes, 

 leading to pigmented or unpigmented photic organs situated on the 

 dorsal surface of the brain, no bicellular glands in the skin, recurved 

 hooks in the introvert either in the adult or at some period in the 

 development. The j^olk-laden prototroch cells of the trochophore 

 degenerate, and their substance passes into the newly formed coelom 

 of the young larva. 



B. Methods. 



Living Phascolosomas, that are removed from the water and 

 covered with a mass of wet eel- grass, remain in a fresh condition 

 even after several hours of transportation. They should be washed 

 free from mud, and placed in large crystallizing dishes full of fresh 

 sea-water. The dishes may be placed either at the bottom of an 

 aquarium, in such positions that the delivery tube shall not send a 

 current directly upon the worms, or the water in the crystallizing 

 dishes may be aerated by a gentle air-stream. An aquarium like 

 those at Roscoff, constructed wàth an upright escape tube, which 

 passes through the bottom of the tank, and which may be easily 

 raised or lowered, is indispensable, for the water in the aquarium 

 thus may be easily kept at a constant low level, and the aquarium 

 may be cleaned quickly without being moved. The dishes which 

 contain the worms should be frequently cleansed of the muddy sand 

 and fecal matter that are voided by the worms. Phascolosoma rarely 

 lays during the first night after its capture. On the second night, 

 when egg-laying is usually to be expected, the intestines have been 

 nearly emptied, and eggs that are free from dirt may be. taken from 

 the bottom of the glass dishes. 



