916 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



As in the maturity of the ova, so the formation and maturity of the 

 spermatozoa indicate the occurrence of puberty. In the human male this 

 takes place about the age of fifteen or sixteen years, and in other mammals 

 it occurs a short time later than the occurrence of fertility in the female of 

 the same species. The appearance of puberty in the male is also attended 

 with certain characteristic signs. The larynx undergoes a rapid increase 

 in size, and, as a consequence, the voice becomes deeper, while hair 

 makes its appearance on the pubes, in the axillae, and on the face. The 

 sebaceous glands become larger and more active. In the male of the 

 domestic animals the appearance of procreativeness is recognized by the 

 occurrence of the capability of erection of the penis and the birth of 

 sexual desires. In the domestic animals in a state of nature sexual ex- 

 citement occurs in the male only at definite periods of the year, but in 

 domestication this makes its appearance whenever a mature male is in 

 the neighborhood of a female of the same species when in heat. 



Impregnation. — Only those mammalian ova become developed into 

 embryos which are fecundated through contact with the male spermatic 

 element, and that this may be accomplished the introduction of the 

 seminal fluid within the internal genital organs of the female is essential. 

 That this process, which is termed coition, may be accomplished the 

 erection of the male genital organ, the penis, is essential in order to 

 permit its penetration within the vagina of the female. 



The penis is composed of the two cylindrical corpora cavernosa with 

 the corpus spongiosum, perforated by the urethra, lying between and 

 below them, these three bodiesbeing held together by fibrous and mus- 

 cular sheaths. The corpora cavernosa, and to a less extent the corpus 

 spongiosum, are composed of erectile tissue, which consists of a tendinous 

 connective-tissue sheath containing thickly woyen elastic tissue and 

 smooth muscular fibres, forming thus a fibrous envelope ; while the in- 

 terior is composed of numerous fibrous interlacing trabeculee, the spaces 

 being in communication with the veins, and are thus to be regarded as 

 venous sinuses. At the outer part of the corpus spongiosum some of 

 the small arteries terminate directly in the outer venous sinuses, while 

 some, however, terminate in capillaries which ultimately reach the venous 

 sinuses, to be collected again in the venous radicals which converge to 

 form the dorsal vein of the penis. 



Erection is accomplished by the overfilling of these venous sinuses, 

 while the engorgement so produced by compressing the outgoing venous 

 trunk serves to prevent the escape of blood from these parts. The 

 overfilling of the blood-vessels of the penis results in a three- or four- 

 fold increase in its volume, while, at the same time, a higher tempera- 

 ture, pulsatile movement, an increased consistence, and erection of the 

 organ results. The first phenomenon in the production of erection is to 



