332 BIOLOGY. [BOOK iv. 



filament long and thin. But the form of the spermatozoary 

 seems to be secondary, for certain animals have simultaneously 

 zoosperms of two different forms, (Paludina vivi- 

 <* para.) 1 The filiform part is the locomotory organ 

 of the spermatozoary. The movements produced 

 by this sort of vibratile cilium are moreover very 

 varied. They are sometimes movements of repta- 

 tion, sometimes movements of torsion, sometimes 

 flutterings, sometimes spirally penetrating move- 

 ments. 2 There are no immobile spermatozoariea 

 among the vertebrates. They seem, however, to be 

 very numerous among certain invertebrates, especially 

 | the crustaceans. But probably their rigidity is only 

 FIG. 53. apparent, and ceases as soon as they penetrate into 

 of rn raan T^a, the body of the female. It is certain that even the 

 e, 6 tai &> b 7 ' mobile spermatozoaries of man and of the mammif erg 

 move with much more velocity when they enter the 

 mucus of the uterine neck or body. Their rate of progression) 

 however, is infinitely less than it appears in the microscope, 

 According to Henle it is only eighteen hundredths of a milli- 

 metre a second in man. The rate of progression varies muct 

 with the nature of the ambient medium. It increases in ar 

 alkaline solution, diminishes, on the contrary, in an acid 

 medium. 



Since the discovery of the spermatozoaries, by Leuwenhoeck, 

 the question has often been asked whether the spermatozoariej 

 were or were not animals. Certain micrographers, partisans ol 

 the first opinion, have gone so far as to assert that the sperma- 

 tozoaries of the mammifers are differentiated animals. Some 

 have even thought that they had testicles. Judged by our present 

 instruments of observation, the spermatozoaries are absolutely 

 without structure, are very inferior in this respect to the vibratile 

 epithelial cells, with which they have been compared. We must 

 consider them special anatomical elements, superior to most of 

 1 Leydig, loc. cit., p. 600. 2 Ibid., p. 554. 



