GERM CELLS OF COELENTERATES 45 



external morphological characters." Nor have we any reason 

 to believe this evolution has ceased. It is quite conceivable that 

 the chromosomes may be tending toward a persistence throughout 

 the entire life of the cell in all its changes, and in some cases may 

 now be distinguishable in interkinesis as well as in mitosis. But 

 the evidence does not warrant a belief in such a continuity as 

 Robertson and McClung postulate for all chromosomes of all 

 organisms. The work of Hance ('17) furnishes him with no 

 evidence of a persistence of individuality during interkinesis, 

 and he can only subscribe to such a view by broadening the 

 present concept. That is, he believes the chromatin particles 

 may persist from generation to generation, but the bodies which 

 they form do not persist. This view could hardly be tested, 

 since we are without means of identifying or following particular 

 chromatin particles at the present state of our technique. If 

 such a belief could be confirmed, we should have a chromatin 

 individuality hypothesis which would be without many of the 

 objections of the present one. 



So far as coelenterate chromosomes are concerned, there is 

 nothing to disprove the view that the chromosomes of one 

 generation are descended from the chromosomes of a previous 

 generation. All the evidence obtainable, however, is quite in- 

 consistent with the view of the persistence of chromosomes as 

 distinct entities during interkinesis. A genetic continuity is 

 very probable, a morphological continuity is highly improbable. 



VI. SUMMARY AND CONCLUSIONS 



In the Scyphozoa and Actinozoa all observations point to the 

 entodermal origin of germ cells. The former widespread belief 

 in the ectodermal origin of germ cells in Hydrozoa cannot be 

 maintained, for literature records show a greater number of 

 species whose germ cells arise in the entoderm than of those in 

 which the ectoderm produces them. The germ cells of Hydrozoa 

 may originate in either or both germ layers ; the same individual 

 may even produce germ cells from both ectoderm and entoderm. 

 There is no characteristic place of germ-cell differentiation in 

 this class. 



