GERM CELLS OF COELENTERATES 3 



every record, which means that a few species have been recorded 

 twice when two authors differ in their results. If these disputed 

 cases were omitted, the ratio would remain practically unchanged. 

 Four investigators, working upon six species, agreed that the 

 germ cells might take their origin either in the ectoderm or in the 

 entoderm; Goette ('07) found five species in which the male 

 germ cells were formed in one layer and the female cells in the 

 other; in fourteen species the two sexes agreed in the place of 

 germ cell origin. Other authors have recorded for single species 

 a different place of origin for the two sexes. 



Those recent investigators who have studied the Hydrozoa 

 most carefully and extensively are in agreement upon the lack 

 of definiteness in the place of germ-cell origin. They agree that 

 the portion of the polyp or colony where germ cells arise is not 

 alw^ays the same, the layer may differ in the same species and in 

 the two sexes of the same species, and they also agree in dismissing 

 the place of origin in germ cells of Hydrozoa as of no significance. 

 The work of the author is in harmony with this opinion. 



2. Time of origin 



The investigation of the precise time in ontogeny at which 

 germ cells arise comes within the scope of cytological study, rather 

 than in earlier embry ©logical investigation. This change of 

 attitude has developed largely as a consequence of the interest 

 in the germ-plasm theory of Weismann; it is of much impor- 

 tance to the theory to determine the time at which germ cells 

 are differentiated and especially to discover their relation to the 

 fertilized ovum. The studies of Weismann ('83) upon the origin 

 of sex cells of Hydromedusae furnished him with the chief material 

 upon which to formulate his theory. The actual observations of 

 Weismann, did not, in fact, w^arrant the enunciation of this 

 theory, as has been clearly pointed out by Goette ('07), C. W. 

 Hargitt ('11), the author and others. It is only necessary to 

 refer to the preceding section to note the extent to which Weis- 

 mann's claim of the ectodermal origin of the germ cells in all 

 Hydrozoa is incorrect; indeed Weismann's own published papers 



