218 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



view implies that the germinal mass is partly somatic in its properties 

 and partly germinal, since it gives rise to both germ cells and somatic 

 structures. According to the second view it is entirely germinal, and is, 

 so far as its remote origin is concerned, directly derived from the ances- 

 tral germ cells of the primitive metazoon, although in comparatively 

 recent times it has become differentiated into two portions, of which one 

 retains its phylogenetic significance, and gives rise to germ cells, while 

 the other produces structures which are only indirectly concerned in 

 sexual reproduction. According to this view, the phylogenetic history of 

 the follicle and the fertilizing duct is different from that of the other 

 organs of the body, which have been represented at each step in the long 

 series of ancestral forms by corresponding somatic structures, while these 

 organs have no remote somatic representatives, since they have been 

 recently evolved as the result of differentiation among the germ cells 

 themselves. 



According to the first view, the follicle cells are no more closely 

 related than ganglion cells or muscle cells to the germ cells, while 

 according to the second view they are homologous with, and were 

 recently equal to or identical with germ cells. 



In a certain sense every cell of the body is homologous with a germ 

 cell, and the difference between the two views concerns the antiquity 

 and completeness of the differentiation, and the time when it is estab- 

 lished in the ontogenetic development of the embryo. 



Seeliger is an advocate of the first view. He says (11, p. 42): "I 

 believe that the young cells of the ovary, which have the power to pro- 

 duce by fission or budding other cells which become converted into the 

 follicle, are not to be regarded as eggs, nor held to be homologous with 

 the primitive, phylogenetic, unicellular stage to which the whole animal 

 kingdom is to be traced back. The production of the follicle is therefore 

 not the beginning, but the last stage of ontogenetic development; the 

 last change which takes place in the body of the metazoon, when it is 

 almost complete, and before it gives an independent existence to the 

 egg cell, in which the species reverts to the primitive stem form." He 

 advances this as a hypothetical explanation of the alleged formation of 

 test cells and follicle cells from ova, although he does not give assent to 

 the statement that this actually takes place. 



Cell multiplication goes on with energy in the embryonic, undiffer- 

 entiated, germinal mass of the salpa embryo, as well as in the corres- 

 ponding embryonic region at the root of the stolon in mature salpa3, and 



