564 MANUAL OF HISTOLOGY. 



The same mechanical obstacles to the motions of the spermatozoa are pre- 

 sented by matters which become simply gelatinous in water; such as 

 vegetable mucous. Those re-agents, also, which act chemically on either 

 the seminal filaments or fluid, as, for instance, mineral acids, metallic 

 salts, acetic acid, tannic acids, ether, alcohol, and chloroform, all bring 

 the lively movements of the former to an end. They may be best exa- 

 mined in serum, white of egg, and vitreous humour ; as also in the contents 

 of the vesiculse seminales, prostate, and Coioper's glands, as the natural 

 ingredients of the semen. In the secretions of the internal female organs 

 of generation their motions are for a long time preserved. Here they 

 may be observed, in the mammalia, wandering hither t and thither for 

 days, under the favouring influence of the animal heat of the parts. 

 The acid mucous of the vagina, as well as the transparent and viscid 

 secretion of the cervix, are said to put an end to the movements of the 

 spermatozoa. Urine,' when neutral or slightly alkaline, has no very great 

 effect upon the latter ; but when strongly acid or alkaline, its action is 

 very well marked. In alkaline milk or mucus the phenomenon of 

 motion is quite evident, while saliva has the same effect on it as water. 

 This is peculiar, bringing all movement rapidly to an end ; but it is pre- 

 ceded by increased activity for a short time, during which the sperma- 

 tozoa hurry about with great rapidity, striking and lashing with their 

 tails. Soon, however, they come to a state of complete rest, when the 

 under end of the filament is usually observed to be folded round the 

 upper portion, like the lash round the stock of a whip. It is an interest- 

 ing fact that such motionless spermatozoa may be again called into 

 activity by surrounding them with saturated solutions, such as those of 

 sugar, white of egg, and common salt, and also, when in too strong solu- 

 tions, by subsequent addition of water, an indication of the important 

 part which endosmosis plays in the phenomenon. 



We have already seen in an earlier section that the caustic alkalies have 

 a most stimulating action on the ciliary motions : the same has been 

 observed by Koelliker to be the case with the elements of semen. 



Recent research has shown that the spermatozoa penetrate into the 

 interior of the ovum in order to impregnate it, moreover, in the mammalia 

 in considerable number. This entrance appears here, as among all the 

 vertebrates, to be effected by the efforts of the spermatozoa, and carried 

 out by the movements of their thinner portion. A special opening 

 (micropyle), to admit them, has not yet been demonstrated in the zona 

 pellucida, but those radiating lines seen on the envelope of the ovum may 

 possibly represent, as pore-canals (52), such passages for the spermatozoa 

 which may be enlarged by the latter. These, on penetrating into the 

 yelk, become motionless, and soon after break down and become fluid. 



286. 



Turning now to the thick-walled vasa deferent-ia, it will be remembered 

 that they take their origin gradually from the passages of the epididymis, 

 and are therefore possessed of a similar structure to the latter. They 

 are made up of an external fibrous investment, then a muscular coat of 

 considerable thickness, composed of three laminae (already mentioned in 

 speaking of the epididymis), an external strong and internal weak layer 

 of longitudinal fibres, together with a middle tunic of circular bundles, 

 which is the strongest of the three. The mucous membrane with which 

 they are lined is covered by columnar cells, O'OSOl mm. in height. Near 



