vj the Ova o/'C'litliuniu.-t. 20o 



when wc carefully consider the subsequent embryonal stages 

 of Chtlionius. I believe that I am not wiDng in tiiinkln;^ that 

 it is the same substance which in a later sta<,^' of the embryo, 

 in which the lirst rudiments of the extremities occur, occupies 

 the internal cavity of the embryo. Jn fact the formation of 

 the albuminoid mass in the interior of the embryo can only 

 be explained l)y a penetration of the albuminous-looking layer 

 into it; the rapid diminution of the layer in the stage just 

 mentioned is in accordance with this. 



As 1 have alreadv mentioned, the nuclei of the spheres of 

 segmentation break up partially into a numlier of granules. 

 In this, however, consists the first step towards the formation 

 of the true blastoderm ; for the granules become surrounded 

 by corresponding portions of protoplasm — a process which 

 represents the first formation of the subsequent blast(^dermic 

 ctdls in the interior of the nutritive vitellus. Just as in the 

 eggs oiP/iilodromus (Ludwig*), the proto])lasm-spherules 

 must here also work out through the deutoi)la3m of the nutri- 

 tive vitellus to its outer surface, which, in fact, really happens ; 

 and the nutritive vitellus (analogously to the portions of deuto- 

 plasm converted into flakes {SchoUen), Ludwig) is already sur- 

 rounded by a continuous layer of jirotoplasm-balls, each of 

 which is provided with a distinct nucleus (figs. VI., />/, & VII., 

 bJi). The protoplasm-spherules thus produced arrange them- 

 selves on the surface, and by mutual approximation and limi- 

 tation form the blastodermic vesicle ; the protoplasm-balls 

 become more and more individualized, and finally form 

 distinctly marked blastodermic cells (fig. VII.). The blasto- 

 derm is then further developed : the cells which have hitherto 

 been separated arrange themselves, so to speak, after the fasliiou 

 of pavement-epithelium, and gradually separate from the 

 nutritive vitellus, whilst at the same time the interspace thus 

 produced begins to fill with a new layer of blastodermic cells. 

 These latter cells (mesodermic cells ?) are larger than those 

 already mentioned, rounded, and geneially full of granules, 

 and accumulate (as Metsclmikoff has already remarked) upon 

 the same part of the embryo on which the provisional appen- 

 dage, described as the *' lip-muscle " by Metschnikoflf fj after- 

 wardis occurs (fig. VII., hl^)' 



Thus I have reached the end of the description of my 

 results relating to the developmental history of the ovum in 

 the ovary and the formation of the blastoflerm of Chthonius. 

 What has been said may be bricfiy summed uj) as follows: — 



The protoplasm gradually becomes filled with primary deuto- 



* Ludwig, /. c. pp. 477 et neqq. 



+ Metwhniki^flT, "Entw. des f'ht/ifrr." I.r. p. ol 7. pi. .xxxviii. fij^r. 9r. 



