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THE MALE GENERATIVE GLANDS. 187 



Innumerable, lively moving, thread-like elements, the so- 

 called seminal filaments, seminal animalculae, spermatozoa 

 (Fig. 164) are here met with, suspended in a hyaline fluid. 

 Their movement was, at an earlier epoch, 

 credulously accepted as a proof of an inde- 

 pendent animal life. The name of the seminal 

 animalculae, spermatozoa, reminds one of that 

 period. 



Nowadays we know that the motility of 

 the seminal filaments is very nearly related to 

 the ciliary motion (p. 35) ; we likewise know 

 that the so-called " seminal animalculae " rep- 

 resent tissue elements, cell derivatives. We 

 are now no less familiar with the motley di- Fi s- l6 4 — Sper- 



J matozoaof the 



versity of forms which these filaments present sh . e ?v : <?> head ; b 



J * middle piece; c, tail. 



in the animal kingdom. 



Let us confine ourselves to the class of mammalia. 



The filamentous, diminutive thing here shows a so-called 

 head (a), then a somewhat thicker, thread-like, middle ap- 

 pendage, the middle piece {b), and finally, extraordinarily 

 thin, and becoming finer, the terminal piece or tail (c). 

 There was formerly no distinction made between these fila- 

 mentous portions. 



Whether this remarkable structure also has an internal 

 complication is not determined, but is improbable. 



The head of the human seminal element appears as an oval 

 disk, somewhat widened backwards, 0.0045 mm. long and 

 about half as much in breadth, and not more than 0.0013 to 

 0.0018 mm. thick. The entire filament may have a length 

 of 0.0451 mm. ; but its terminal end is infinitely thin and dif- 

 ficult to recognize. 



In the fruitful copulation, the seminal filaments penetrate 

 the zona pellucida of the ovum, conducted through the very 

 fine porous canals of this envelope (Fig, 158, a), and pass 

 into the yolk, that is, into the true ovum cell. They here 

 finally disintegrate by fatty degeneration. 



The process of division which we have already mentioned 



