THE MALE REPRODUCTIVE ORGANS. 



215 



FIG. 260. 



already mentioned, the marked vibratile movements of the seminal 



filaments are most characteristic. 



The spermatozoa are minute highly-specialized elements, each 

 of which bears at one end a long cilium of exceeding delicacy : 

 while differing greatly as to details of form and of size 

 among vertebrated animals, the mammalian sperma- 

 tozoa possess in common three more or less dis- 

 tinctly defined parts, the head, the middle-piece, 

 and the tail. 



The human spermatic filament possesses an 

 entire length of 50-60 /*, of which the head con- 

 tributes 3-5 fji, the middle-piece 

 4-6 /*, while the remaining 43-49 y. 

 belong to the tail. 



The head varies in form accord- 

 ing to the side examined ; when 

 seen on its broadest surface it is 

 egg-shaped, the broader end of 



the head being directed anteriorly, Human spermatozoa Human spermatozoa 



and the Smaller end being" COn- as usually seen: a, from highly magnified : h, m, 



, ., . .,,. . the broader surface ; b, t, respectively head, 



neCted With the middle-piece. f rom the side; c, ele- middle-piece, and tail; 



Seen in profile, the head is COn- ment with remains of f, elements seen from 



. . . spermatoblast adhering the broader surface; p. 



cavo-convex, and terminates in a to middle-piece. from the side, 



blunt rounded anterior extremity. 



The greatly diminished middle-piece is connected with the posterior 

 pole of the head, and on the other hand fades away into the long 

 delicate caudal filament. After the action of certain reagents the 

 middle-piece splits up into a number of fibrillae of great tenuity (Bal- 

 lowitz) ; in spermatozoa not entirely matured spiral fibrils are some- 

 times observed in this part of the element. The centre of the sper- 

 matic filament is occupied by the delicate axial fibre, which connects 

 the head with the middle-piece and extends through the middle-piece 

 and the tail. Immediately behind the head, at the beginning of the 

 axial fibre, lies a minute nodule, the end-knob ; this body probably 

 represents the equivalent of the centrosome of the spermatoblast. 

 Within the middle-piece the axial fibre is ensheathed by a delicate 

 envelope. 



The characteristic vibrations of the spermatic filaments may con- 

 tinue for a long time after ejaculation : when suitably prepared, and 

 under favorable conditions, these cells retain their vitality for many 

 hours and even days. Human spermatozoa, mounted under cover- 

 glasses and protected from evaporation, have been observed by the 

 author to exhibit distinct vibratile motion after the lapse of over nine 

 days. After death these elements may continue to vibrate for forty- 



