556 A. C. WALTON 



C. THE FERTILIZATION PROCESS 



The fertilization of the nematode egg, especially that of A. 

 megalocephala, has been studied carefully by many observers, 

 the chief among whom are Schneider ('83), Van Beneden ('83, 

 '87, '88), Nussbaum ('84), Boveri ('87 b,'87 d,'88 a, '90), Zacha- 

 rias ('87 a, '87 b, '87 c, '87 d, '12), Kultschitzky ('88 a, '88 b), 

 Hertwig ('90), Sala ('94), Meyer ('95), Carnoy et Lebrun ('97), 

 Erlanger ('97), Retzius ('12 b). Held ('12), Romeis ('12), and 

 Vejdovsk}' ('12). Fertilization in the dog ascarid A. mystax 

 was early studied by Nelson ('52), Bischoff ('55), Meissner ('55), 

 Thompson ('56), Claperede ('58), and Munk ('58). Later Car- 

 noy ('87), Kultschitzk}' ('88 c), and Lukjanow ('89) studied the 

 same process in A. marginata, and Marcus ('06) in "A. canis 

 (sp. mystax)," which he believed to be identical with the A. 

 marginata of the earlier writers. Glaue ('08) has maintained 

 that the names A. canis, A. marginata, etc., are all synonomous 

 with the older term A. mystax Zeder; however, it seems ex- 

 tremely doubtful whether A. canis and A. marginata are identi- 

 cal species. 



The work of the early observers on the ascarids of the dog 

 was, of course, confined to the more superficial events of fer- 

 tilization. Nelson ('52), Bischoff ('55), and Thompson ('56) 

 maintained that the spermatozoon merely came in contact with, 

 but did not enter, the egg, and by this contact initiated segmen- 

 tation. Meissner ('55) believed he saw the sperm enter the egg 

 through a micropyle. He also was the first to suggest that the 

 refractive body of the sperm was of a nutritive character. This 

 has recently been shown (Marcus, '06; Wildman, '12; and Wal- 

 ton, '16 c) to be the correct interpretation. The existence of a 

 definite micropyle for the entrance of the sperm was denied by 

 Claperede ('58), but he supported the idea that the sperm en- 

 tered the egg, claiming that the sperm was passively forced 

 into the egg substance by a contraction of the oviduct wall. 

 Munk ('58) defended the existence of a micropjde and also 

 maintained that the sperm entered the egg through its own ac- 

 tivities. Carnoy ('87), Kultschitzky ('88 c), and Lukjanow 



