II Jan., 1909.] 



FAcments of Animal Fh vsiology. 



The cells that give rise to spermatozoa in the testes are laid aside for 

 this purpose at a very early stage of development — long before birth — but 

 they do not become active until puberty which takes place at an age 

 varying with each species. The i-roduction of spermatozoa is not the only 

 function that the testes carry out ; these two glands are undoubtedly the 

 seat of formation of chemical messengers or hormones which pass into the 

 blood stream and influence most regions of the body. At puberty, beside 

 sexual power and desire, a number of secondary characters cccur in the male 

 such as changes in the ^•ocal chords and larynx giving the broken voice, 

 increased growth of hair, increased muscular, mental and emotional 

 activity, &c. , which are referable to hormones derived from the* testes. If 

 an animal be castrated before puberty these secondary sexual characters 

 do not appear ; in such an animal however development of these niissing 

 characters can be stimulated by grafting a testis from a male of the same 

 species somewhere in the body. 



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Fig. 62. Fertili/atiou of an Ovum, Highly Magnified. - I. A nuinl)er of 

 spermatozoa have readied the border of the ovum. An alteration in the tunic of the 

 ovum takes place opposite ihe foremost spermatozoon. II. and III. Stages in the 

 entry of the foremost spermatozoon ; the others are refu^-ed admittance. (After 

 Hagemann ) 



The ova are formed in the two glands of the female called ovaries. The 

 cells from which the ova arise are already laid aside in the mammal long 

 before birth, but do not become active until puberty is reached. After 

 this age until sexual activity ceases, a process of ripening of the ova can 

 be observed in each ovary. (Fig. 6^.) From time to time an ovum sinks 

 in the ovarian tissue and gets enclosed in a 'hollow sphere of cells or 

 FOLLICLE containing a fluid ; this .sphere gradually works to the edge of the 

 ovary and then bursts, liberating the ovum into the abdominal cavity. 

 This process, ovulation as it is called, will occur if access is denied to the 

 male but though not entirely dependent upon the sexual cycle it is hastened 

 both by the state of the genitalia in the period of oestrus or sexual desire 

 and by copulation with the male. The ovum in the abdominal cavity in 

 some m.anner not thoroughly understood is carried (pO'Ssibly in a purely 

 passive way by the writhing of the pelvic gut) to the mouth of one of the 

 two FaMopian tubes. It is then apparently seized by the tentacular mouth 

 of the tube and driven slowly towards the uterus bv peristalsis. Should 

 no spermatozoon be present the ovum passes through the uterus and thence 

 into the vagina and so is discarded. But should a spermatozoon enter into 

 the ovum fertilization will occur. When the spermatozoon bores into the 



