914 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



of the glands of the vas deferens, of Cowper's glands, of the prostate 

 gland, and of the vesiculae seminales. It contains water, varying from 

 80 per cent, to 90 per cent, in different animals, serum-albumen, alkali albu- 

 men, nuclein, lecithin, cholesterin, fats, salts, especially the phosphates 

 of the alkaline earths, with sulphates, carbonates, and chlorides, and 

 a peculiar odorous principle the nature of which is unknown. 



When examined with the microscope it is found that the seminal 

 fluid may be divided into a plasma and formed elements. The constit- 

 uents already mentioned constitute the plasma of the semen and the 

 formed elements are the so-called spermatozoa, and it is the latter which 

 are the active elements of the secretion in the function of reproduction. 



Fig. 415.— Spermatozoa. (Landois.) 



1, human (X 600), the head seen from the side ; 2, on edge ; Tc, head ; m, middle piece ; /, tail ; c, ter- 

 minal filament. 3, mouse, i, bothriocephalus latus. 5, deer. 6, mole. 7, green woodpecker. 8, black 

 swan. 9, from a cross between a goldfinch (m) and canary (/). 10, cobitis. 



Each spermatozoon consists of a flattened or pear-shaped head, fol- 

 lowed by a rod-shaped middle piece with a long, tail-like prolongation, or 

 cilium. When examined shortly after extrusion from the testicle, the 

 cilium is found to be in rapid vibration, and by this motion the entire 

 spermatozoon is propelled forward at the rate of about half a millimeter 

 in a second. The movement of the spermatozoon is identical with that 

 of other forms of ciliated movement and is affected in the same way by 

 the same reagents. At first the movements are active, and, under favor- 

 able circumstances, they come to rest only after two or three days. The 

 spermatozoa of different animals differ in shape and size, as is shown in 



