324 KING. [Vol. XVII. 



number of spermatozoa in the hope of confirming Field's ('96) 

 results on the echinoderm spermatozoon, that a slight depres- 

 sion exists in the anterior end of the head in which the centro- 

 some lies. All attempts to discover such a depression in the 

 spermatozoon of Bufo have failed to show other than a sharp 

 oniward curving line between the head and the apex, and if 

 a centrosome is present in this part of the spermatozoon it 

 is imbedded in the substance of the head and is too minute to 

 be detected. 



At the posterior end of the head is the so-called " middle- 

 piece" (Fig. 41, M), a cylindrical rod 0.012 mm. long andb.006 

 mm. wide. After the use of iron-haematoxylin, this portion of 

 the spermatozoon appears uniformly homogeneous and perfectly 

 colorless, showing no sign of any structure that might be con- 

 sidered a centrosome. In all cases the middle-piece appears to 

 be sharply differentiated from the head, and if a projection 

 from it extends into the head as found by Ballowitz in the 

 spermatozoon of Triton, and by Fick in that of Axolotl, its 

 presence cannot be detected in the spermatozoon of Bufo len- 

 •tiginosus, owing to the deep staining of the substance of which 

 the head is composed. 



Fick has conclusively demonstrated for Axolotl that the 

 "attraction spheres" in the fertilized egg arise from the mid- 

 dle-piece of the spermatozoon. He has stated that it is the 

 whole middle-piece which stains an intense black with iron- 

 haematoxylin, the apex and head remaining absolutely colorless. 

 This result is in striking contrast to that obtained on the sper- 

 matozoon of Bufo lentiginosus by the use of iron-haematoxylin. 

 In this case the head alone stains black, the apex, middle-piece, 

 and tail remain uncolored. If, as maintained by Heidenhain 

 ('92) and others, iron-haematoxylin is a specific centrosome 

 stain, then it follows that the middle-piece of the spcrmatosoon 

 of Bufo lentigijwsus does not contain a centroso^ne, and that, if 

 one is present, it must be imbedded in some part of the head. 



The tail of the spermatozoon of Bufo varies from 0.28 mm. 

 to 0.37 mm. in length. It consists of two thread-like fibers 

 which come out from the center of the lower surface of the 

 middle-piece. One of these fibers is shorter, straighter, and a 



