The germ-cells. 619 



Introduction. 



Part I of the "The Germ-Cells", now published, was completed 

 in the summer of 1900, and text and plates were then finished. It 

 does not mark the close of the research even into one form, Raja 

 hatis. Indeed, it may be described as a preliminary survey of the 

 field in this animal, and as treating more especially of the distribution 

 of the primary germ-cells. It represents the fruits of some four 

 months of intense study : it has also been followed by a much longer 

 period of investigation, some 15 months ; in which time, while Baja 

 hatis has by no means been neglected, other forms, such as ScylUum 

 canicula^ Pristiurus, Torpedo, Acanthias, and the chick, have come 

 more or less under review. 



As the result a considerable material of observations and some 

 drawings have accumulated, and, it is hoped, that the first part of the 

 work may be followed by a second, not the final portion, within 

 a short time. 



For the skate the third part of the work will treat more fully 

 of the cleavage, the number of the germ-cells, and their migrations. 



But for considerations of time and money it would have been a 

 very easy matter to have illustrated the memoir with hundreds of figures, 

 so extensive is the material studied. 



Though written down 18 months ago, and though ever since then 

 the writer has been investigating germ-cells, nothing would appear to 

 require alteration in the manuscript beyond the number of mitoses 

 between cells of 0.03 and 0,05 mm and those of 0.02 mm. As this 

 and allied questions would be fully dealt with in Part III or IV, its 

 consideration may be postponed. 



It had been intended to review the important work of Wilms 

 upon the "embryomas" at greater length, but it may be mentioned, 

 that shortly after the publication of my results in the Anat. Anz., 

 V. 18, a very interesting review from Bonnet's^) pen appeared. In 

 this Wilms' embryomas also receive consideration, and, in the mean- 

 time at any rate, it may not be necessary to add anything more to 

 what Bonnet and the writer have already written concerning Wilms' 

 researches upon these pernicious but interesting structures, the 

 embryomas. 



1) Bonnet, R., Griebt es bei Wirbelthieren Parthenogenesis? in 

 Ergebn. Anat. Entw., V. 9, for 1899, p. 820—870, 1900. 



Zool. Jahrb. XVI. Abth. f. Morph. ^1 



