122 THE DEVELOPMENT OF 



prevented any saccular invagination and the formation of an 

 actual archenteron. This view is good as far as it goes ; 

 but, as will readily be seen, it leaves some points unex- 

 plained. 



Tichomiroff's final paper on the development of the silk- 

 worm (*82) is unfortunately buried in the Russian lan- 

 guage, and all ordinary students must clepend upon ab- 

 stracts for their knowledge of its contents, together with 

 an inspection of the cuts in the text and the figures on the 

 plates ; there being, fortunately, no distinctively Russian 

 method of drawing. The blastoderm is formed by a mi- 

 gration of cells to one pole and the neighboring sides of 

 the egg (vide fig. 11, p. 28). Not all the cells thus come 

 to the surface but some remain behind in the yolk. These 

 are distinctively amoeboid in shape and form, the "primitive 

 entoderm." With regard to the "secondary eutoderm" he 

 agrees with Bobretzky. After the formation of the am- 

 nion and serosa and their union over the germinal area, the 

 primitive groove appears, deeper and more symmetrical 

 in front than behind (vide figs. 14 and 15, p. 33). It 

 later closes, but not completely behind ; but before its clos- 

 ure the mesoderm appears from both ectoderm and ento- 

 derm, and not only from the region beneath the primitive 

 groove, but from all parts of the ectoderm. There is noth- 

 ing in the sections figured to warrant the statement that 

 the mesoderm has such a wide origin ; the arguments for 

 it in the text remain sealed. 



Weismann ( J 82) describes the early stages in several 

 species (Rhodites, Biorhiza, Chironomus, Gryllotalpa). 

 The account, so far as statements of facts go, is most de- 

 tailed with Rhodites. Here we have to do with two ele- 

 ments : the ordinary cells, all of which migrate to the surface 

 to form the blastoderm ; and the two"polkeru,"one of which 

 is placed at either pole of the egg. From the anterior of 



