30 GEORGE T. HARGITT 



• Loeb ('15), who has given much attention to the study of 

 cancer cells, discusses the matter from that point of view. He 

 concludes that the observations of fourteen years upon cancerous 

 growths have established certain facts which are contrary to the 

 view of the radical difference between germ cells and body cells. 

 In those cases where it has been possible to detect and study the 

 earliest indications of cancer in mice, he has been able to trace 

 the transformation of the normal tissue cells into the abnormally 

 proliferating tumor tissue, and is thus able to demonstrate the 

 origin of the tumor from the tissue. He believes that germ cells 

 and somatic cells are not so different, and possess no such 

 differences in potency as is often claimed. 



6. Summary and conclusions 



The germ cells of Hydrozoa are differentiated, at a time just 

 preceding sexual maturity, from different regions of the animal 

 or colony, there being no one region or layer which characterizes 

 the place of origin in this group. These germ cells probably 

 arise in all cases from tissue cells; in some species such an origin 

 is demonstrated, since an entire cell or half a divided body cell 

 produces a single egg or sperm cell. 



Budding in Hydra and hydroids involves a multiplication and 

 growth of the cells and an evagination of all the body layers in 

 the budding zone. The claim that latent germ cells are re- 

 sponsible for budding is not sustained by observations. Some 

 medusae reproduce asexually by budding, and as a rule such 

 buds are produced in a manner similar to that of hydroids, viz., 

 by an evagination of both ectoderm and entoderm. In a few 

 cases asexual buds of medusae arise from the ectoderm alone, 

 but in no case does such a development come from a single cell. 

 Buds may also come from the reproductive organs of medusae, 

 but all investigators of this manner of budding agree upon the 

 activity of ectoderm and entoderm cells of that region; such a 

 process is not a development from germ cells. The different 

 types of budding in Hydrozoa suggest an evolution of repro- 

 ductive processes which may still be in progress. The phe- 

 nomena of budding give evidence of a considerable degree of 



