Hyatt.] 148 [March 5, 



tinction (visible?) between the central cells which are useless and 

 the peripheral cells which bear the spermatozoa, that they differ 

 only in position and that it is more reasonable to suppose that the 

 cells becoming earlier developed would necessarily assume a 

 peripheral arrangement, and not only prevent by their excess of 

 development the growth, but even occasion the degeneration, of 

 the internal cells. This might be in a certain sense perfectly 

 acceptable as an explanation of the way in which the peripheral 

 mode of growth arose, but it is difficult to explain the evident 

 eagerness of the spermatozoa to enter the eggs, or the tendency 

 of the spermonucleus to unite with the feminonucleus of the ovum 

 upon any supposition which does not assume heredity as its basis. 



If this be true, the appearance of this process in the ovum during 

 the agamic stage exhibits an earlier inheritance of a characteristic 

 which in the Protozoa occurs only after and as a result of impreg- 

 nation, except in some of the more specialized Flagellata and 

 Ciliata, where the existence of spermatocysts and spermato- 

 zooids leads one to anticipate a corresponding differentiation in the 

 female zoon, which appears to be in reality an ovum, and to de- 

 velop, like an ovum, into a blastula, as pointed out by Butschli. 



The vitelline membrane seems to have been considered as a dif- 

 ficulty in the way of homologizing the ovum and the body of an 

 encysted Protozoon . Dr. Minot, in a paper as yet unpublished, has 

 homologized the wall of a cj^st, and the zona pellucida of the ovum 

 with each other (Science, Vol. iv, 1884, p. 339). We feel naturally 

 doubtful whether this comparison can be proven, but we do not, on 

 the other hand, consider it at all necessary, that such close com- 

 parisons should be made between purely adaptive parts like the 

 protective coverings of the ovum and the structureless cyst wall of 

 the Protozoon. The cellular membranes of the pouches in which 

 the ova and spermatocysts are isolated and developed in the 

 Porifera are verjr instructive in this connection. The ovum and 

 spermatocyst must make room for themselves, and provide at the 

 same time necessary food for their early growth and it is well 

 known that these reproductive bodies are predacious cells which 

 doubtless grow at the expense of the neighboring cells. They 

 can, therefore, be regarded as having a decidedly irritating action 

 upon the adjoining tissues. This process of continued irritation 

 would be sufficient to cause the flow of wandering cells to and 



