EARLY DEVELOPMENT OF GRANT1A COMPRESSA. 281 



Vacuoles collect near the region of the sperm, and the path of the latter 

 into the egg becomes marked by an area formed of more liquid substance 

 (PI. 20. figs. 13 and 17). The fine yolk-spheres keep closely around this area, 

 but do not invade it, as is shown in PL 20. fig. 13. Subsequent to the entry 

 of the sperm, the oocyte undergoes maturation giving off two polar bodies. 



24. The Fate of the Middle-piece or Sperm Macromitosome (" Nebenkern") 



during Fertilization . 



In Ascaris and Fhallusiaithas been shown that the mitochondrial substance 

 in the middle-piece of the spermatozoon does not degenerate during fertili- 

 zation, but retains its faculty for growth and division and apparently takes 

 some minor part in the phenomenon of fertilization (14). 



With Champy-Kull technique the middle-piece of the Grantia sperm 

 stains a bright red, while the egg-cytoplasm is a greenish or golden-grey 

 colour ; it is, nevertheless, a somewhat difficult matter. to ascertain exactly 

 what becomes of this body during fertilization. Between the stages of 

 PL 20. fig. 12 and fig. 13, the middle-piece in its form of a bun-shaped bead 

 completely disappears. In PL 20. fig. 17, MAM, it is quite clear that the 

 middle-piece is breaking up into a cloud of small granules which adhere to 

 the growing male pronucleus like the tail of a comet. In subsequent stages 

 I never found any granules which I could identify for certain as having 

 originated from the macromitosome, but in PL 20. fig. 13, at x, are certain 

 grains which might be the remains of the original middle-piece. While I 

 do not wish to deny that there may be activity of the male mitochondria 

 subsequent to the stage of PL 20. fig. 17, I consider that such is unlikely. 

 The evidence either way is not complete enough to allow me to express a 

 definite opinion. 



25. The Mitochondria in the Development of Grantia eompressa; 



In certain Ascidia it is established that the mitochondria become unevenly 

 segregated into different blastomeres, the myoplasm being formed mainly 

 from these granules. The two regions of the sponge amphibia stula do not 

 contain granules in equal quantity, and it is interesting to ascertain whether 

 in Grantia there is any special segregation of cytoplasmic granulations into 

 special blastomeres. 



Subsequent to fertilization in Grantia eompressa, the mitochondria become 

 more or less evenly spread out in the endoplasm (PL 21. fig. 21), and 

 during cleavage the distribution of the mitochondria between the blastomeres 

 is equal, as shown in PL 21. figs. 19. 20, 21, and 22. 



In PL 21. fig. 22, the blastula is found to be formed of cells, all of which 

 contain approximately equal numbers of mitochondrial grains. It is only 

 much later during the differentiation of the two main cell-layers in the 



