OBSERVATIONS ON DEVELOPMENT OF COMMON TROUT. 119 



Bambeke describes the " couche intermediaii-e "as consisting 

 of a granular protoplasm, the granules being much larger 

 than in the embryo-cells. The thick portion of the " couche 

 intermediaire " includes constantly a certain number of nuclei 

 and cells, which Bambeke believes to develop by endogenous 

 cell-formation. Bambeke finally concludes that the "couche 

 intermediaire" is the lower portion of the germ-disc, split off 

 from the latter in consequence of the fecundation; it does 

 not undergo cleavage like the upper portion, i. e. the blasto- 

 derm a (Auct.)."^ 



From what has been said previously we can modify 

 already now a portion of these statements. Another portion, 

 that referring to the hypoblast, we shall have to discuss 

 hereafter. 



The only mention of cells outside the blastoderm made by 

 Oellacherii refers to a " not inconsiderable numbers of cells " 

 (1. c, p. 12), which having become separated from the lower 

 surface of the blastoderm during the formation of the seg- 

 mentation cavity remain on the floor of this latter (compare 

 on this subject Rieneck^s paper, my first communication on 

 the development of the trout's ovum, and Strieker's article 

 " On Development of Simple Tissues," in Strieker's ' His- 

 tology^), and " graben sich in die oberflachlichsten Schichten 

 des Dotters ein." Besides this there are found cells also out- 

 side the region of the segmentation cavity ; these Oellacher 

 thinks may have migrated 'there from the former place, or may 

 have become separated from the lower surface of the blasto- 

 derm where this is in contact with the yolk. These cells 

 remain for a very long time in the yolk. Oellacher found them 

 (1. c, p. 13) very numerous, even after the heart was formed 

 and while the vessels of the yolk-sac are being developed; espe- 

 cially in the hind part of the embryo they are very numerous. 

 They enlarge while the embryo proceeds in its development, 

 and are of very various shapes. In longitudinal sections 

 through the embryo these cells form long strips below the 

 former; they also undergo multiplication. Oellacher further 

 mentions (1. c, p. 17) that in certain stages of the development 

 of the subgerminal cavity the most superficial layer of cells 

 of the blastoderm extends for a short distance on the surface 

 of the yolk beyond the blastoderm ; this, Oellacher goes on 



* This " couche intermediaire " of Van Bambeke cannot be compared, 

 as is done in the Reports in the ' Jahresbericht fiir Anatom. und Phy- 

 siol.,' for 1S72, p. 78, with the " basale masse " of Oellacher (see 

 above), for this is only the deep part of the blastoderm, which undoubtedly 

 undergoes segmentation though somewhat later than the part situated more 

 superficially. The " couche intermediaire " of Van Bambeke does not 

 segment. 



