^6 WHEELER. [Vol. V 1 1 1 . 



Among those who take a decided stand on the relations of 

 the vitellophags to the definitive entoderm, Graber and Cholod- 

 kowsky may be mentioned. Graber ('89, p. lo), after intro- 

 ducing the superfluous and inapplicable term " centroblast," ^ 

 says : Dabei nehme ich zugleich, was indessen kaum misbilligt 

 werden diirfte, stillschweigend auch an, dass dieses gegenwartig, 

 wie es scheint, von der Darm- and Gewebsbildung ausgeschlos- 

 sene Zellenlager auch friiher niemals eine dem echten Ento- 

 derm anderer Thiere entsprechende Rolle inne gehabt habe, 

 sondern vielmehr dem letzteren gegeniiber ein neues, wahr- 

 scheinlich mit der starkeren Entwicklung des Dotters im 

 Zusammenhang stehendes Differenzirungsproduct ist." 



Cholodkowsky ('91*) docs not dismiss the matter so briefly. 

 Like Graber he draws a hard and fast line between primary 

 and secondary yolk-cells, and admits no phylogenetic continuity 

 between the vitellophags and the definitive entoderm. The 

 vitellophags belong to none of the germ-layers. His reasons 

 for not regarding them as a precociously segregated portion of 

 the entoderm are neither new nor conclusive. Like other 

 recent investigators he admits that the vitellophags are in part 

 digested or discharged from the alimentary tract along with 

 the remains of the yolk after hatching. But he is not satisfied 

 that the yolk-cells should play a humble role in the insect 

 economy. Some of them were predestined to a higher function 

 than yolk-liquefaction — viz: to give rise to the blood, the fat- 

 body and even to the germ-cells. He therefore supposes that the 

 vitellophags are undifferentiated cells. But this supposition is 

 not supported by the facts. That they are on the contrary, 

 considerably specialized is shown by their limited function and 

 mobility, their gradual and prolonged growth (especially in 

 some Orthoptera), their inability to undergo caryokinesis or 

 even akinesis, and their suspicious relations to the bacteria- 

 like corpuscles of Blochmann. On a priori grounds we should 

 not expect to derive whole sets of tissues from such specialized 

 elements. 



1 Superfluous because we have enough names for these cells already, inap- 

 plicable because the termination "blast" is properly applied only to cells or 

 tissues of a germinal character — not to decrepit elements like the yolk-cells. 



