200 J. S. NICHOLAS 



between the way in which the coat acts, but there is a definite specificity 

 in the way in which the tissues act, whether they are coated or uncoated. 



Schechtman ('34) discovered the general process of ingression. 

 Schechtman placed stains upon the vegetal region of the egg and found 

 that they disappeared. When he came to examine his eggs further he 

 found that the stain had proceeded upward into the floor of the archen- 

 teron going into the blastocoelic floor and that there was a distinct 

 variation as to how far the material would progress according to the 

 stage at which it was placed upon the outside. If the stain was placed 

 upon the unfertilized egg it extended up into the floor of the blastocoele. 

 If it was so placed later, after thirty-two cells, it was just in the lower 

 portion of the floor of the blastocoele, extending to a very slight degree 

 outside the region of the cortex in which it was originally located. The 

 study of ingression seemed so important that it was deemed necessary 

 to carry the study through to the place where Vogt ('29) had stained 

 the early gastrula and followed the movements of particular parts. The 

 study has since been repeated by Nieuwkoop ('46) who confirms, in the 

 main, the results which were brought out by Schechtman, with one 

 minor variation. Since Nieuwkoop stains his materials in many cases 

 considerably later than Schechtman, he got a very distinctly different 

 picture of the final disposition of the stained material. When the stain 

 is applied early, it may proliferate according to extension action effects 

 by which it proceeds directly up the cleavage furrows, the so-called 

 centrifugal effect which Schechtman noticed when he repeated his 

 earlier results. This, however, is not a normal effect, but rather a diffu- 

 sion one, and the reaction of the egg must be measured in terms of its 

 diffusion constants as well as the changes to diffusion which are under- 

 gone according to its degree and state of development during the seg- 

 mentation stages. 



Similar results are attained in my own study of this phenomenon 

 (Nicholas ('45) ). In my material, however, there is one step which can 

 be added. There are two distinct steps in the ingression system, the first 

 arising as described by Schechtman and the second occurring in those 

 specimens which are stained deeply and carry a second part of the stain 

 on the surface. It proceeds through the ventral lip and there is invagi- 

 nated, sometimes by apposition staining the dorsal lip. It is most promi- 

 nent in the floor of the archenteron and eventually merges with the 

 material which was formerly in the blastocoelic floor forming a con- 

 tinuum with it. The primary ingression is blastocoelic, the secondary 

 a gastrocoelic floor contribution. The first ingression forms the anterior 



