No. 2.] THE EGG OF BUFO LENTIGINOSUS. 323 



If the fundamental cause of reduction is alike for all forms, 

 the conflicting results which have been obtained from a study 

 of oogenesis and spermatogenesis in both plants and animals 

 obviously cannot be explained by the theory advanced by Weis- 

 mann. Strasburger ('94) has recently asserted that : " The 

 morphological cause of reduction in the number of chromo- 

 somes, and of their equality in number in the sex cells, is phylo- 

 genetic. There is a return to the original generation from 

 which, after it had obtained sexual differentiation, an offspring 

 was developed having a double number of chromosomes. It is 

 not the outcome of the gradually evolved process of reduction, 

 but the reappearance of the primary number of chromosomes 

 as it existed in the nuclei of the generation in which sexual 

 differentiation first took place." To this hypothesis, which 

 was expressed in substance by Whitman in 1876, Wilson ('96) 

 has raised objections, and a satisfactory solution of the problem 

 seems as remote now as when, in 1891, Boveri stated: "Dass 

 uns aber eine wirkliche Einsicht in diesen Vorgang bis 

 jetzt fehlt. Es bleibt weiterer Forschung vorbehalten, dieses 

 Dunkel aufzuhellen." 



IV. The Spermatozoon. 



The spermatozoon of Bufo lentiginosus greatly resembles 

 that of Bufo cinereus as described by La Valette St. George 

 ('96), and is similar in all essential respects to that of Alytes 

 obstetricans (Ballowitz, '90). The head (PL XXX, Fig. 4.1, H), 

 which is usually slightly sickle-shaped, is a cylindrical struc- 

 ture 0.1 1 mm. long and 0.08 mm, thick. It stains an intense 

 black with iron-haematoxylin and a deep red with the combina- 

 tion stain used, and appears perfectly homogeneous in all its 

 parts. The anterior end of the head is slightly rounded and is 

 perfectly distinct from the apex, which is an awl-shaped struc- 

 ture 0.025 mm. long, ending in a fine point (Fig. 41, A) and 

 showing no affinity for either iron-haematoxylin or the combina- 

 tion stain. As the anterior end of the head or the base of 

 the apex apparently contains the centrosome, if one is present 

 in the spermatozoon, I have very carefully examined a large 



