378 s. HATTA : 



layer of the lateral plate ; the segmental duct is looked upon as 

 of the epiblastic origin. 



GoETTE ('90) worked the development of Petromyzon fluvia- 

 tilis ; his results with respect to the pronephros show some agree- 

 ment with mine, especially those concerning the later stages. The 

 author derives also the whole system of the pronephros (including 

 the segmental duct) solely from the mesoblast. But we diverge in 

 some important points from each other ; he has found the earliest 

 traces of the structure at a time when the rudiment of the heart 

 first becomes apparent (his vi. Periode) (p. 64). From the account 

 given in the foregoing pages it is clear that this period belongs 

 to a later stage in wdiich the pronephros has already made a 

 considerable progress in development ; his figures 99, 103, &c., 

 which are spoken of as representing the first appearance of the 

 structure, approximately correspond with my figures 82, 83, &c., 

 and with those of even older stages. 



The pronephros is, according to Goette, not of a separate 

 Anlage in its first appearance, but arises in a form of a longi- 

 tudinal furrow formed, on each side, by an evagination of the 

 parietal layer of the mesoblast ; the lips of the furrow being fused 

 at certain points, there remain three openings ; these are 

 converted afterwards into three tubules and ciliated funnels. 

 The tubules are added by stages until there are usually five, or 

 more rarely four or six ; but how these are multiplied, he can 

 not say with certainty. The tubules have, it seems to him, no 

 relation to the metameres of the body ; for 3 to 5 tubules are 

 found in the extent of 2 to 3 metameres (loc. cit., pp. 64-65). 



Th(:' .segmental duct originates, according to Goette, in pre- 

 cisely the same way as tlie pronephros proper ; the only diflerence 

 is the complete constriction of it from its mother-layer just as 



