ANATOMY OF BIRDS 



323 



placental mammals. No prostate or Cowperian glands exist in 

 birds. 



The sole office of the testis, or ooj)horon masculinvm, is the 

 secretion of semen, associate structures being simply accessory for 

 the conveyance of that vital substance and its transference to the 

 opposite sex. The seminal fluid itself is 

 merely the vehicle of transport of the sperma- 

 tozoa, in which their activity may be freely 

 exercised in their intuitive struggles to gain 

 access to their mates in the ovary. It is 

 literally a " sea of life " in which the minute 

 creatures swim in shoals to their destiny — 

 and their fate in any case is death. If they 

 successfully buifet the waves of fate they iind 

 a watery grave in the ovum at last; if that of ^domesttc lo^e^kTTr'^t?^ 

 haven be not reached they simply perish in wl'nS^an/LeuckMt"' ""^"^ 

 mid-ocean. The spermatozoa, or seminal 

 animalcules, or male Dynamamoebce (Figs. 106, 107), are the 

 exact counterparts of ovarian ova, in so far as they are single-celled 

 animals of a very low grade of organisation ; but their activity and 

 intelligence are marvellous, and still more so is the mysterious attri- 

 bute with which they are endowed of assimilating their protoplasmic 

 substance with that of the ovum ; with the result that the thus 

 fecundated ovum is capable of procreating itself 

 by fission for a period until a mass of similar 

 creatures is engendered ; from which mass is then 

 speedily evolved the complex body of the Bird. 

 The corresponding female Dynamamcebce (ovarian 

 ova) are simple spherical animalcules, physically 

 indistinguishable from an ordinary encysted Amaba; 

 but the spermatozoa are remarkably distinguished 

 in appearance, furnishing probably the best marked 

 case of sexual characters to be found among the 

 Protozoa, to which class of animals they belong. The 

 spermatozoa resemble flagellate infusoria or ciliated 

 endothelium cells, though they each have but a 

 single whip. They are of extremely minute size, much smaller than 

 their females, and filamentous ; more or less thickened and some- 

 times wavy at their nucleated heads, whence protrudes an excessively 

 delicate thready tail, endowed with great vibratory energy. They 

 may be likened to diminutive attenuated tadpoles, which swim by 

 lashing the tail in the seminal fluid. Under the microscope shoals 

 of these curious creatures may be seen swimming in the sea, nosing 

 about in search of the ovum, butting their heads in wrong places, 

 backing out and trying again in another direction ; with such success 



Fio. 107.— Sper. 

 matozoa of sparrow, 

 greatly maguified ; 

 from Owen, after 

 Wagner and Leuok- 

 act. 



