126 BR. E. KLEIV. 



cuneiform accumulation to the other, wedged in between the 



fat globules of the yolk. 



As regards the later stages, I may now be very brief. In 

 all stages I found the parablast present as more or less con- 

 tinuous membranous masses, forming at numerous places 

 cuneiform or prismatic or irregular shaped accumulations, not 

 only underneath the embryonal portion, but also in all other 

 parts of the archiblast. Its (parablast) aspect remains 

 always the same, i. e. a finely granular material containing 

 isolated, or, as is more commonly the case, groups of nuclei. 



We have thus far been able to ascertain that one part of 

 the germ, viz. the parablast at first situated outside the 

 area of the archiblast (blastoderma, Auct.), gradually 

 encroaches on the surface of the subblastodermic yolk, due 

 partly to the growth of the blastoderm over the parablast, 

 and partly due to an active growth of this latter itself, so 

 that after a certain time the subblastodermic or segmentation 

 cleft becomes lined on its floor with parablast. 



There remain now two other points to be discussed : 

 (a), the substance of which the parablast is composed and the 

 nuclear elements found in it; and (b) the relation of the 

 parablast to the cells on the floor of the segmentation cavity 

 and to the elements of the archiblast in general. 



(a) The substance of the parablast is, as has been men- 

 tioned on several previous occasions, a finely and uniformly 

 granular substance, showing this slight difference in the 

 earlier and later stages, that it is more transparent in the 

 latter than in the former. (In this, as in the preceding, we 

 mean by "parablast" only that portion which is at first 

 situated in the vicinity of the edge of the archiblast, and, 

 as has been shown, gradually grows inwards underneath the 

 archiblast, so as to line the floor of the segmentation cavity.) 



Whether the appearance of fibrillation which is to be 

 observed in some parts of the surface of the parablast is 

 due to a real fibrillar arrangement of its substance, or is 

 only produced by the hardening reagent, must remain 

 undecided. 



The outlines of the parablast are not well defined towards 

 the yolk, especially when the parablast has grown inwards 

 on the yolk of the saucer-like depression ; this is chiefly due 

 to the fact that the yellowish granules which are contained in 

 the yolk — yolk granules — are gradually shading off" into the 

 smaller granules contained in the parablast. To suppose 

 that on account of the deepest part of the parablast con- 

 taining granules which insensibly pass into the larger 

 granules of the yolk, the two substances, i. e. parablast and 



