No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 47 



But a more weighty objection may be adduced. It has been 

 shown by Heider ('89) and Heymons ('9o), not to mention many 

 previous investigators, that the fat-body and sexual-cells arise 

 from the mesoderm, and my own studies fully confirm this view. 

 Concerning the origin of the blood there is some doubt, but it 

 should be stated that Cholodkowsky has made no satisfactory 

 observations of his own on this point and that, although some 

 facts point to a derivation of the blood from the yolk-cells, 

 others as definitely point to its origin in the mesodermal layer. 



After taking for granted that the vitellophags are undiffer- 

 entiated cells, that they have nothing and, what is more, never 

 have had anythmg to do with the entoderm, and that they give 

 rise to blood-corpuscles, adipose-tissue and germ-cells, Cholod- 

 kowsky ushers in the parablast theory. It was to have been 

 hoped that this theory might have been permitted to end its 

 days in peace within the confines of vertebrate embryology 

 where it originated. Fortunately, however, it has grown too 

 old and decrepit, even under the skillful medical treatment 

 which it has received from time to time, to be of any service 

 in invertebrate morphology. 



There is something almost ludicrous in Cholodkowsky's ap- 

 plication of the parablast theory to the Insecta when we con- 

 sider the methods which he employed in preparing the yolk of 

 the Blatta ^^g. The capsules opened at both ends were sub- 

 jected to the action of undiluted Perenyi's fluid for 12 hours 

 and the eggs after treatment with the customary grades of 

 alcohol, cleared in green cedar oil 24 hours. Thence they 

 were transferred to paraffine (55-60° C.) and left 3-5 hours. 

 The result of this heroic method is apparent enough in the dis- 

 tortion of the tissues, but its effect on the yolk is quite 

 remarkable. 



Both Blochmann ('87) and myself ('89) described the yolk of 

 the Blatta o.^^ as consisting of a mass of homogeneous and 

 granular albuminoid bodies sharply polygonal from mutual 

 pressure and interspersed with spherical oil-globules. We also 

 described a peculiar distribution of the polygonal bodies; those 

 of a homogeneous nature constituting an oval central core in- 

 vested with the granular bodies. I further claimed that the 



