The germ-cells. 631 



In Plate 44 there are drawings of seven others in a degenerate 

 condition, and to these seven yet one more must be added, the peculiar 

 case of Figs. 46 and 47. 



Adding, then, the eight degenerate germ-cells to the total we 

 obtain 512. This number would be obtained by 9 synchronous di- 

 visions from one cleavage-product; or, of course, by 8 such of 2. 

 Probably, therefore, the germ-cells of this embryo arose by 9 divisions 

 from one cell of the cleavage. 



512 represents the normal, abnormally placed, and degenerate 

 germ-cells present in this particular embryo of 32 mm i). It may be 

 pointed out, that in earlier periods of the development there may 

 have been others, which have degenerated and disappeared. The 

 writer, however, offers no opinion on this point. 



The abnormally- placed germ-cells of embryo No. 454 number 155, 

 if those found in degeneration be left out of account. Before con- 

 sidering this number, and comparing it with the figures obtained from 

 other embryos, it may be advisable to define more exactly what is 

 meant by the term "abnormally-placed germ-cells". It will be ad- 

 mitted without cavil, that any germ-cell situated in any position, 

 other than in the so-called germinal ridge, is not in the place, where, 

 according to our present morphological ideas, it ought to be. At a 

 time, when, as in this embryo, the "germinal ridges" are well developed 

 (Fig. 37), they might be expected a priori to contain any or all of 

 the germ-cells already present. This is the case in no single one of 

 my numerous embryos of less than 45 mm; and, indeed, this fact 

 alone is sufficient to cast grave doubts on the accuracy of the cur- 

 rent view, according to which the germ-cells one and all arise from 

 the epithelium of a restricted area of the peritoneum. 



No embryo of less than 45 mm ^) is free from abnormally-lying germ- 

 cells; and, be it added, the number, or the percentage of such, is 



1) Of all my embryoi^ of earlier years this one was, owing to the 

 stain and comparative thickness of the sections, an especially favourable 

 one for this enumeration. To carry this out in a series of cases will 

 entail the preparation of specially thick sections. Time has since writing 

 been found to do this (compare Part III). 



2) It is not suggested, that in embryos of upwards of 45 mm all 

 the germ-cells are in normal situations. My work on older specimens 

 has not yet been extensive enough to satisfy me on this head. In 

 R. radiata No. 268 (51 mm) none could be found in abnormal positions. 

 In the degree of its development this specimen represents a R. baits 

 of upwards of 70 mm, i. e., a young skate. 



