40 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



make their appearances as differentiated areas of the blastoderm 

 before the lower layer is produced, his observation appears to have 

 been in error. 



While Tikhomirowa (1892) discusses the origin of the mesoderm 

 at considerable length, her ideas are also inaccurate. Her paper is 

 primarily a criticism of Patten's article on the embryology of Neo- 

 phylax (1884) in which he describes the mesoderm as originating 

 from cells which migrate inward from the midventral blastoderm, the 

 same method as has been described above for the middle region of 

 the germ band in the case of fleas. Tikhomirowa did not base her 

 observations on any of the Trichoptera, but insisted that, contrary to 

 Patten's observations, it must arise in Ncopliylax in the same manner 

 she claimed to observe it originate in the flea and in Chrysopa. She is 

 emphatic in her assertions that in both of these insects the mesoderm, 

 and the lining of the mesenteron as well, are derived from the yolk 

 cells (trophonuclei). Her views on this subject are clearly described 

 in a translation of her own words : 



In summing up my observations on the formation of the ectoderm and primary 



entoderm, viz, the blastoderm and yolk cells respectively I must contend 



that here the process is different from that described by Patten in regard to the 

 phryganids which he studied. In examining his figures and comparing them 

 with my own, I find a great deal of resemblance between them. For this reason, 

 it seems to me that that author was mistaken in affirming that all the cleavage 

 cells go into the formation of the blastoderm. It is very possible that he did not 

 notice the negligible number of segmentation elements which remain in the 

 interior of the vitellus at the beginning of the formation of the blastoderm and 

 which remain in the center multiplying rapidly and giving rise to the primary 

 entoderm. In regard to the formation of the mesoderm I have several series of 

 slides which show definitely that its cells are derived from the primary entoderm 

 (vitelline cells). If we should study one of the preparations representing the 

 germ band, we would remark that the primitive groove is very indistinct, so that 

 in this stage there is not the slightest possibility of the separation of a part of 

 the ectoderm (blastoderm) for the formation of the mesoderm. In sections of 

 eggs of the same stage, we see that the mesoderm is very distinctly set off from 

 the ectoderm. Directly below the ectoderm are situated cells of the mesoderm, 

 one right next to the other. Here we can follow clearly all the transitions of the 

 nuclei of the primary entoderm, or rather of the nuclei of the vitelline cells, 

 by their size, form, and coloration, even to the mesoderm close by. On this point, 

 also, my observations differ from those of Patten who states for the phryganids 

 that all the mesoderm is derived from the blastoderm cells in the region of the 



primitive groove I find in the earlier as well as later stages of Pidex 



serraticeps, incontestable proof of the fact that the mesoderm is derived from 

 the primary entoderm or vitelline cells. The series of slides of Pulcx serraticeps 

 which I possess, shows the formation of the mesoderm from its initial stage 

 and proves beyond doubt that the first cells of the mesoderm are nothing else 

 than the cellular elements remaining behind in the interior of the egg after the 



