GERM CELLS OF COELENTERATES 7 



the supporting layer to the enteric cavity. In some (gl) the 

 cytoplasm bordering the cavity stains differently than the deeper 

 part of the cell; these are gland cells. Other cells do not extend 

 to the cavity, and still others, while they extend to the enteric 

 cavity, do not show such a differential staining capacity. Some 

 of these are gland cells, while the interpretation of the others is 

 uncertain. 



The study of entire stems in optical section is necessary and 

 very helpful in determining the number, size, shape, and distri- 

 bution of the egg cells, but lack of sharpness in such prepara- 

 tions, especially with high powers, makes it impracticable to 

 secure positive evidence concerning the finer details of structure 

 of the smaller cells. Such evidence must be gained from the 

 study of sections; this will be described very shortly. 



A second problem possible of elucidation by the study of entire 

 stems concerns the migration of germ cells. Weismann ('83, 

 '04) claims the egg cells arise only at the distal end of the main 

 stem and at the distal ends of the chief branches, from which 

 points there are extended migrations into the gonophores. I do 

 not understand this to mean that after a colony has become 

 mature the germ cells begin to form from the young cells at the 

 distal ends of branches and migrate throughout the colony to the 

 gonophores, which are especially abundant toward the base of the 

 colony. Such a migration does not occur, for the main stem and 

 the basal ends of the larger branches are always devoid of egg 

 cells, which could hardly be the case if egg cells moved from 

 the distal ends of branches to the lower branches. Weismann 

 states in his earlier works that egg cells may only migrate dis- 

 tally, never proximally, though the contrary is implied in the 

 figures and descriptions of his later discussions (Weismann, '04, 

 vol. 1, p. 414). I take it, rather, that he means the germ cells 

 arise in the young parts of the colony, migrate toward the re- 

 gions where gonophores are to be produced and upon their appear- 

 ance the egg cells take their position in the gonophores. 



The migration just outlined would not be very great in ex- 

 tent, and it is probable that some such movement takes place. 

 The egg cells on the right of figure 4 are elongated as though 



