612 GEORGE T. HARGITT 



guished here the only way for such cells to get to the budding 

 medusae would be by- a migration along the radial canals or 

 through the jelly of the bell. They could not escape notice in 

 these places since the cells of the canals and tentacles are very 

 unlike germ cells. 



The study of Hybocodon is directed mainly to an investigation 

 of this continuity of the germ plasm, and no attempt is made 

 at a complete study of the cycle of the germ cells, but where any 

 facts are obtained bearing on conditions found in other forms, 

 they will be set forth. 



MATERIAL 



The material on which this study is based was obtained by 

 several persons, in different seasons, and at different places. 

 By towing a net through the waters of the harbor at Woods 

 Hole, in Vineyard Sound and vicinity some material was secured. 

 However, the greater part was gathered by the author while 

 on a dredging trip with the U. S. Fisheries Steamer Fish Hawk. 

 The vessel being anchored, during a fog, in the main channel 

 near Crab Ledge and the Stone Horse Shoals, east of Chatham, 

 the tow nets were lowered into the strong tide current which 

 was running and great numbers of the medusae were collected 

 both from the surface and from a depth of several fathoms. 



The technic of fixation included formalin, fluids containing 

 mercuric salts, picric acid, osmic acid, and the like. The for- 

 malin fixation was excellent for general morphology but was not 

 very favorable for cytological study. The mixtures were all 

 fairly satisfactory except for a shrinkage of the jelly of the bell 

 which occurred in all of them; in Bouin's fluid there was less 

 shrinkage, and mercuric chloride mixtures also gave very good 

 results. Sections have been made longitudinally and also trans- 

 versely through the entire medusa, and the study has included 

 careful examination of all sections from the aboral end of the 

 bell to the tentacles, in order to guard against overlooking 

 migrating cells. 



