OBSERVATIONS ON DEVELOPMENT OF COMMON TROUT. 121 



widerlegt.' " But only a few pages later (p. 102) he says, 

 that there exist, however, other discoblastic ova in which 

 that portion of the food yolk which lies next to the blasto- 

 derm participates also in the segmentation, and produces 

 cells which become partly blood-cells, partly connective-tissue 

 cells ; in doing so Haeckel maintains that Goette " hasproved" 

 (Max Schultzse's 'Archiv,' vol. x, 1872) that in the dis- 

 coblastic bird's ovum segmentation extends also into a por- 

 tion of food yolk ; in this are produced cells — " yolk-cells," 

 which become used " partly as blood-cells, partly as food for 

 the developing embryo;" likewise Haeckel takes it that 

 Balfour '• has shown " that, in Elasmobranch fish, a large 

 portion of food yolk undergoes segmentation; and, finally, 

 E. Ray Lankester ('' Development of the Cephalopoda : " see 

 this Journal, 1875^ No. LVII) "has seen" in the discoblastic 

 ova of Cephalopods numerous cells originate in the food 

 yolk, which therefore undergoes secondary cleavage.] 



We proceed now with our own observations. 



The next stage I wish to describe is that represented in 

 fig. 2. The archiblast consists of nucleated embryo-cells, 

 the most superficial layer of which contains large cells of an 

 opaque substance. The segmentation has proceeded (as is 

 seen in fig. 2) to a considerable extent; the shape of the 

 archiblast is that of a biconvex disc, thicker, however, at 

 one edge than at the other; its thickness in the centre is 

 over 0'5 mm., its breadth over 1*4 mm. The archiblast is 

 in its whole extent resting on, but at the same time very 

 sharply defined from, the yolk, which latter appears in 

 hardened preparations as if limited by a membrane. Under- 

 neath the archiblast the yolk contains large oil drops and 

 yellowish granules; the latter become larger in size, the 

 farther away from the surface of the yolk. The paragerminal 

 groove above mentioned is still distinctly seen. Next to this 

 groove, and in immediate contact with the archiblast (see fig. 2) 

 extends the parablast outwards on the surface of the yolk, gra- 

 dually becoming thinner as it becomes more distant from the 

 archiblast. The most conspicuous part is the thickened por- 

 tion of it (parablast), which, as is shown in fig. 2, presents in 

 vertical section a more or less triangular shape ; that is, it cor- 

 responds to a prismatic body, of which Van Bambeke (see 

 above) correctly observes that it surrounds the archiblast like a 

 ring-shaped rim. But Van Bambeke is not correct in saying 

 that this mass has an outer, inner, and lower surface, for it has 

 an outer, inner, and upper surface ; nor that it extends as a 

 thin layer over the saucer -like depression of the yolk; and 



