the Seminal Fluid of Animals. 333 



during the pairing- season of these animals, this result appeared 

 to me at first extremely remarkable. Dissection afterwards re- 

 vealed the cause of this apparent anomaly. Among animals 

 of this kind, whose lives last only for a single summer, and 

 particularly among butterflies, it by no means happens that all 

 individuals possess the power of procreation. This is most 

 strikingly seen in the females, many of which, even in autumn, 

 have ovaries containing immature ova. Still the motions ob- 

 servable in the seminal fluid of invertebrate animals are never 

 so lively as those observed in the semen of the vertebrate. 

 Had I not occasionally seen, in the case of the former, these 

 organized bodies change their forms by evident contractions 

 and extensions, I should certainly think they were without any 

 motion dependent on internal causes. I have observed these 

 changes of form particularly in the organized parts of the male 

 semen of the Cantharis livida, which I had killed during co- 

 pulation, and then immediately opened. This observation of 

 mine on the microscopic bodies observed in semen, is sup- 

 ported by the observations made by earlier writers, that the 

 semen of very young, of very old, and of hybrid animals, as, 

 for instance, the mule, does not contain any seminal animal- 

 cules. 



" The second of my observations is, that although the orga- 

 nized parts of semen possess a proper motion, they are also car- 

 ried onwards by currents which take place in the Jiuid portion of 

 the semen. The same observation was also made before me by 

 Von Gleichen, but did not attract any notice, notwithstanding 

 its strong claims to attention. This motion occurs only at the 

 period of heat. T have seen the most striking examples of it in 

 the semen of frogs, which I had opened shortly after awaking 

 from the state of hybernation. It is consequently not entirely 

 peculiar to the seminal fluid of warm-blooded animals, in which 

 it was noticed by Von Gleichen. It exhibits itself but feebly in 

 undiluted semen ; this, however, arises from the viscid nature 

 of that fluid. Still the seminal animalcules manifest even in 

 feeble motions, but the latter become exceedingly energetic 

 the moment a small quantity of water is added to a drop of se- 

 men placed on the porte-objet of the microscope ; they continue, 

 however, only a short time. 



