574 GENERATION AND DEVELOPMENT. 



comparison with the size of the spermatic artery, the blood 

 must move very slowly. 



The seminal fluid secreted by the testicle is one of those se- 

 cretions in which a process of development is continued after 

 its formation by the secreting cells, and its discharge from them 

 into the tubes. The principal part of this development con- 

 sists in the formation of the peculiar bodies named seminal fila- 

 ments, spermatozoa or spermatozoids (Fig. 213), the complete 

 development of which, in their full proportion of number, is 

 not achieved till the semen has reached, or has for some time 

 lain in, the vesiculse seminales. Earlier, after its first secretion, 

 the semen contains none of these bodies, but granules and 

 round corpuscles (seminal corpuscles), like large nuclei, in- 

 closed within parent-cells (Fig. 213). Within reach of these 

 corpuscles, or nuclei, a seminal filament is developed, by a 

 similar process in nearly all animals. Each corpuscle, or nu- 

 cleus, is filled with granular matter ; this is gradually con- 

 verted into a spermatozoid, which is at first coiled up, and in 

 contact with the inner surface of the wall of the corpuscle 

 CFig. 213, C, 1). 



Thus developed, the human seminal filaments consist of a 

 long, slender, tapering portion, called the body or tail, to dis- 

 tinguish it from the head, an oval or pyriform portion of larger 

 diameter, flattened, and sometimes pointed. They are from 

 5- j- th to gj^th of an inch in length, the length of the head 

 alone being from 70 Vi) ta to ^oVo tn f an i ncn > an( * i ts width 

 about half as much. They present no trace of structure, or 

 dissimilar organs ; a dark spot often observed in the head, is 

 probably due to its being concave, like a blood-corpuscle. 

 They move about in the fluid like so many minute corpuscles, 

 with each a ciliary process, lashing their tails, and propelling 

 their heads forwards in various lines. Their movement, which 

 is probably essentially, as well as apparently, similar to that 

 of ciliary processes, appears nearly independent of external 

 conditions, provided the natural density of the fluid is pre- 

 served ; disturbing this condition, by either evaporating the 

 semen or diluting it, will stop the movement. It may continue 

 within the body of the female for seven or eight days, and out 

 of the body for at least nearly twenty-four hours. The direc- 

 tion of the movement is quite uncertain ; but in general, the 

 current that each excites keeps it from the contact of others. 

 The rate of motion, according to Valentin, is about one inch 

 in thirteen minutes. 



Respecting the purpose served by these seminal filaments, 

 or concerning their exact nature, little that is certain can be 

 said. Their occurrence in the impregnating fluid of nearly all 



