THE SEMEN. 191 



The spermatozoa of the tritons and salamanders usually lie 

 coiled up in the form of a ring, and seem to spin round 

 as upon a pivot ; at the same time a second wavy and 

 tremulous motion, like that produced by ciliae, is observed ; 

 this arises from the rapid rotatory or spinning movement of 

 the very delicate tail with which the spermatozoa of these 

 animals are furnished, and which is wound spirally round the 

 body. Wagner at one time entertained the notion, which 

 however he subsequently discarded, that the wavy motion 

 referred to was produced by a ciliary apparatus. Some- 

 times the coiled spermatozoa have been seen to unrol them- 

 selves and to cross the field of the microscope with slow ser- 

 pentine motions. 



Furthermore, in the various motions executed by the sper- 

 matozoa they exhibit all the characters of volition ; thus they 

 move sometimes quickly, at others slowly, alter their course, 

 stop altogether for a time, and again resume their eccentric 

 movements. These movements it is impossible to explain 

 by reference to any hygroscopic properties which may be in- 

 herent in the spermatozoa, they appear to be so purely 

 voluntary. A strong argument, therefore, in favour of the 

 independent animality of the spermatozoa may be derived 

 from a consideration of the nature of their motions. 



Duration of Motion. 



The length of time during which the motions of the sper- 

 matozoa continue, either after the escape of the seminal fluid, 

 or after the death of the animal, varies very considerably ; 

 thus it is maintained for a longer period in warm weather 

 than in cold, and when the semen is retained within its 

 natural reservoirs than when it is removed from those re- 

 ceptacles. The spermatozoa of some animals also preserve 

 their powers of locomotion for a longer period than those of 

 others ; thus the seminal animalcules of birds die very soon 

 after the death of the bird ; according to Wagner, frequently in 



