SPERMATOZOA. 75 



X. Spermatozoa. 



The seminal elements of tailless Batrachians Lave 

 received a great share of attention, not only on the 

 part of anatomists and physiologists, but even of 

 systematic workers. This is clue to the great amount 

 of difference in structure and size between these 

 elements in the various genera; and also to the fact 

 that otherwise closely allied species of the genus Rana 

 may differ in their spermatozoa more considerably 

 from each other than from others morphologically 

 more remote. The failure to obtain hybrids between 

 such near allies as the male Rana temjporaria and the 

 female R. arvalis has been attributed principally to 

 these differences ; for other species of the genus Bufo, 

 which stand very far apart, but which have almost 

 identical spermatozoa — as, for instance, B. vulgaris and 

 B. calamita, and B. vulgaris and B. viridis — cross with 

 comparative facility under artificial fecundation. 



One great source of errors in describing and com- 

 paring the spermatozoa has been due to the changes 

 which these elements undergo in their development, 

 and care should be taken to ascertain whether or not 

 they are in a ripe condition. The safest way to avoid 

 mistakes is not to extract the spermatozoa from the 

 testicles, but to collect them in the seminal ducts 

 from specimens in embrace. This is, however, difficult 

 to do in species which are destitute of a seminal 

 bladder. 



Thanks to the investigations of Leydig, La Valette 

 St. George, Spengel, and Pfliiger, which I have been 

 able to supplement for some of the less known species 

 of Rana, we are now well acquainted with the sperma- 

 tozoa of nearly all the European species. 



Those of Discoglossus are remarkable for their great 

 size, measuring three millimetres, whilst those of other 

 species do not exceed one-tenth of a millimetre. The 

 so-called head is spirally wound like a corkscrew ; the 



