224 GEyEEAL ORNITHOLOGY. 



of appearance as they present under diflferent circiunstances is mainly seasonal. For birds, 

 as a rule, procreate only at particular times of the year, rarely having more than one or 

 two broods of young : the functional activity and quiescence of the testes correspond, as the 

 enormous swelling of the gland during the breeding season is one of the peculiarities of the 

 bird's organ. This may be related to the absence, in birds, t>f specially formed vesiailce semi- 

 naks, or seminal reservoirs ; though certain contortions and dilatations of the sperm -ducts 

 which are to be observed may imperfectly answer to detain the secretion until circumstances 

 render it available. The passage of the sperm-duct is alcmg the face of the kidneys, generally 

 iu company with the ureters ; the opening is by a papilla upon the surface of the uro-genital 

 sinus. These papillose terminations of the sperm-ducts are erectUe to a degree, and answer the 

 purpose of paired penes in those birds which are not provided with better-formed copulatory 

 parts. In coitu, th»; cloacal chambers containing the orifices of the genital ducts are opened, 

 and the more or less jirotruded papillae come in contact or close juxtaposition. In cases in 

 which a penis or two penes are developed, the urethral passage is a groove, never a tube, 

 though cavernous and even muscular tissue may be developed ; and iu any case of such an 

 intromittent apparatus, it has cloacal invagination when not operative (see p. 891). These 

 organs, in all their variety, are of the sauropsidan, not mammalian, type ; though in some 

 respects the structure approaches that seen in the non-placeutal mammals. No prostate or 

 cowperian glands exist in birds. 



The sole ofiice of the testis, or oophoron masculinum, is the secretion of semen, associate 

 structures being simply accessory, for the conveyance of that vital substance and its transfer- 

 ence to the opposite sex. The seminal fluid itself is merely the vehicle of transport of the 

 spermatozoa, 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 

 buffet the waves of fate they find a watery grave in the ovum at last ; if that haven be not 

 reached they simply perish in mid-ocean. The spermatozoa, or seminal animalcules, or male 

 Di/namamcebce (figs. 106, 107), are the exact counterparts of ovarian ova, in so far as thoy are 

 single-celled animals of a very low grade of organi- 

 zation ; but their activity and intelligence is marvel- 

 lous, and still more so is the mysterious attribute 

 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 mato7oa'ofsparrow. 



of rloniestic cock, greatly , -r.. , m, ,. n t -i-v i ..i -^ i 



magnified; from Owen, after the Bird. The correspondmg female DynamamcehcB ^H^^^^^^^'^'f^'^^^ 

 Wagner and Leuckart. (ovarian ova) are simple spherical animalcules, phys- -wagner andLeuck- 



ically indistinguishable from an ordinary encysted ^Wfce&rt; but the sperma- art. 

 tozoa 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 sometimes wavy at their nucleated heads, whence pro- 

 trudes an excessively delicate thready taU, endowed with great vibratory energy. They may bo 

 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 that out of myriads a score or so may gain tlieir end. It 



Fk; mo. —Spermatozoa --«-- ;- *i J:i i..«J ^u- -. i-- i,...n. „f Fig. 107. Sper- 



