MITOCHONDRIA ASCARIS. 259 



granules at the time of the completion of the refractive body than there 

 were in the early spermatids. The greater number of these granules, 

 or plastochondria, are clustered around the nucleus, although a few 

 of the smaller ones are found scattered throughout the cytoplasmic 

 sheath that covers the refractive body (Fig. 12). These are most 

 plainly seen in spermatozoa in which the refractive body has been 

 partially or entirely used up (Figs. 13 and 14). After having been 

 carried into the egg with the sperm, the larger of the plastochondria 

 can be distinguished for some time after the sperm nucleus has left 

 them and set up its own vesicle preparatory to uniting with the female 

 pronucleus (Fig. 15). These granules slowly fuse with, and become 

 indistinguishable from, the granules of the egg cytoplasm by the time 

 the two pronuclei have united, although occasional cells show a few 

 of the plastochondria still distinguishable at this time (Fig. 16). 



Meves believes that these plastochondria are the 'plasma bearers 

 of heredity' because they fuse with similar granules in the egg cyto- 

 plasm. In order to prove that they may be such ' bearers,' satisfactory 

 answers must be found to several perplexing c^uestions that are as yet 

 unanswered. One of these is the question as to the nature of the ' cyto- 

 plasmic reduction.' In this reduction a great many of the plasto- 

 chondria are lost. To prevent the loss of parental qualities borne by 

 these granules it must be that there either is a selective division, — so 

 that only plastochondria bearing duplicate characters are cast ofP, — 

 or else the larger granules, which remain near the nucleus and are never 

 lost, are the only ones that carry hereditary ciualities. The first sup- 

 position is not substantiated by facts thus far brought out and hence 

 must be abandoned. The second- supposition, that the hereditary 

 qualities are borne by the larger plastochondria, has been invalidated 

 by the work of Vejdovsky, in which he has shown that, inasmuch as 

 these plastochondria entirely lose their identity, they are in no way 

 continuous from generation to generation and hence can not be bearers 

 of hereditary qualities. 



The work of Lillie on Nereis is also an argument against the function- 

 ing of the plastochondria as bearers of hereditary qualities, for he finds 

 that the plastochondria of the sperm do not even enter the egg, but, 

 with the tail-piece, remain outside. The classical work of Boveri on 

 the fertilization of enucleated egg fragments also shows that the plasto- 

 chondria of the female do not carry hereditary qualities. These 

 granules unite with the corresponding ones of the male. Now, if 

 the latter carry male characteristics, we should be justified in supposing 

 that the female granules would similarly carry female characters, since 



