DEVELOPMENT OF PARAVORTEX GEMELLIPARA 525 



with which it was earher associated may still be detected, al- 

 though less easily than during the period of its activity. 



A certain fact favors the view that a process of disintegration 

 has attacked the mitochondrial substance. For whereas, up 

 to the time when the entoderm cells had absorbed a considerable 

 amount of yolk, the body appeared conspicuously in iron- 

 haematoxylin material, it has been found impossible to detect 

 it in such preparations at later stages of development. This 

 peculiarity, taken in connection with the ability of the Ehrlich 

 stain to bring it out subsequently, points to the conclusion that 

 the mitochondrial substance has become chemically changed. 

 Furthermore, no trace of it is to be observed after the yolk 

 globules have been transformed into such a fluid mass as noted 

 in the upper entoderm cell of figure 42. It would be too extreme 

 to surmise that the mitochondrial mass represents a substance 

 laid down in the oocyte for the purpose of acting as a digestive 

 agent after the yolk has been taken inside the embryo. Such 

 an interpretation would have to regard the substance as a poten- 

 tial ferment, which, before it could act upon the yolk, must 

 undergo a transformation which renders it invisible. 



Against the view that this mitochondrial mass is functional 

 at this stage is the evidence furnished by the ectoderm. Here 

 a simultaneous yolk-digestion has been in progress where none of 

 the mitochondrial substance entered. In figures 35 and 37 

 each posterior epithelial cell contains one or more of the large 

 fluid spheres. In appearance and reaction to the Ehrlich's 

 haematoxylin-eosin stain, these masses are closely similar to those 

 in the entoderm. As we have seen, their origin also is the same. 

 In the iron haematoxylin preparations, however, the ectodermic 

 material stains brownish while the entodermic masses are color- 

 less. It is probable that both substances are lipoids of some 

 sort. 



After the young worm has left the capsule and is prepared to 

 take food through the mouth the reserve material present up to 

 this time in the ectoderm rapidly disappears. The process is 

 apparently one of gradual absorption and assimilation. In 

 one preparation a cell just beneath and closely applied to the 



