576 A. C. WALTON 



complete development of the potential organ so localized. The 

 work of Loeb on artificial parthenogenesis has shown that eggs 

 can develop, apparently in a normal manner, without, the pres- 

 ence of a spermatozoon. Normal or facultative parthenogenesis 

 also is of somewhat common occurrence. From this it would 

 seem that all the necessary traits of the organism are borne in the 

 egg itself, and the traits, if any, borne by the sperm are superfluous. 

 The fact that practically no male cytoplasm ordinarily enters 

 the egg with the sperm seems to indicate that it has little or no 

 function in fertilization. However, in Ascaris, as in all nema- 

 todes, the sperm nucleus is surrounded by a comparatively large 

 amount of cytoplasm, the possible role of which in the fertihza- 

 tion process is yet to be demonstrated, but can not a priori be 

 denied simply because it has not yet been found. Partheno- 

 genetic nematodes are frequently found, however, and this may 

 be an argument for the non-functioning of the sperm cytoplasm 

 as a necessary factor in the transmission of hereditary traits. 



From these facts it seems that the conception of fertilization 

 as expressed by Marcus ('06), Zacharias ('13), and others — that 

 is, fertilization taking place only in the 'resting nuclei' of the 

 daughter cells of the first cleavage division — is too limited. 

 Fertilization may, and perhaps does, begin the instant the sperm 

 cytoplasm comes in direct contact with that of the egg by the 

 breaking down of the sperm-membrane — even earlier, if we 

 accept the osmotic theory of cytogamous fertilization as shown 

 by some amoebae — and may continue until the chromosomes 

 of the two daughter cells of the first cleavage division have re- 

 formed after their 'resting' condition. Fertilization is thus a 

 process which may extend over a long interval, and can not be 

 limited to any one definite period or place in cell development. 

 Cleavage, incited by the centrosome brought in by the male, 

 may thus begin before the process of fertilization is completed. 

 As is commonly the case in most nematodes, the two pronuclei 

 in A. canis do not ordinarily fuse into one definite 'fusion nucleus' 

 before the first cleavage spindle is established. Of the hundreds 

 of cells observed, only two such ' fusion nuclei' were found. 

 The more common method of procedure was that of direct 



