312 THE ANATOMY OF CESTODES. 



and distend it to such an extent that one is tempted to speak of 

 distinct sperm sacs. Sometimes straightly extended, and sometimes 

 more or less tightly wound, the canal runs in a transverse direction 

 (Fig. 158), or perpendicularly downwards (Fig. 159), according to the 

 position of the porus genitalis, and ultimately breaks up into a number 

 of thin, delicate canals, which sooner or later, and often after repeated 

 ramification, meet the little testes, and are united with them. 



The anatomical condition of these vasa efferentia is largely deter- 

 mined by the distribution and number of the testes, both which factors 

 are subject to extraordinary variations. In the larger species many 

 hundred testes (Fig. 158) are found, consisting of clear and round 

 little bladders. These are each surrounded by a clear, structureless, 

 glassy membrane,^ and contain tufts of spermatozoa, or the cells in 

 which these are formed, in different stages of development,^ and are 

 pretty equally distributed over the whole joint. But as the size 

 diminishes, so does the number of the testicles. Instead of a hundred, 

 perhaps only some dozens are then found, as in Tmnia perfoliata 

 (Fig. 162, A), where they are situated in what 

 appear to be two rows upon the vas deferens 

 behind the sperm sacs ; or they may be reduced 

 to smaller numbers, even down to two or three, 

 as is especially the case in certain FcenicB of 

 birds, such as T. setigera (Fig. 160,^), and also in 

 Fig. 161.— Generative T. unciuata of the shrew-mouse (Fig. 161). 



organs of JVema urecimato rrii , • n ,i , , ■ «. , i ti 



(after Stieda), showing The emptying of the testes is effected, hke 



receptaculum (5), germ- that of the vas deferens, by means of the 



gland [d), yolk-gland (c), - . , , , 



testes (A), and oirrhus- muscles ot the body, but the two processes are 

 pouch (/). (x25.) apparently accomplished by different groups. 



While the testes are principally subjected to the pressure of the 

 transverse and sagittal fibres, which run through the surrounding 

 tissue, all the more abundantly, since this is converted into a cubical 

 meshwork by the formation of the above organs, it appears to be 

 mainly the longitudinal and transverse fibres which act upon the vas 

 deferens, and discharge its contents into the cirrhus-pouch. 



1 While this glassy membrane originates in the structureless connective tissue, the 

 spermatozoa are produced ■ by a metamorphosis of cells, which in no way differ from the 

 young connective-tissue cells. In other words, the testes, like the other viscera of these 

 animals, are only differentiations of the body - parenchyma (mesoderm). Thus we oivn 

 understand the statement of Moniez (Bull, Scient. dep. Nord, p. 221, 1878) that the 

 formation of the spermatic elements takes place in the meshes of the body-parenchyma, 

 and not in a special organ. In the same way, he denies the presence of special vasa 

 efferentia, and thinks that the spermatozoa make their own way through clefts previously 

 formed in the tissue. 



^ Moniez has made the structure of these spermatozoa the subject of special investiga- 

 tion, VInstitut, July 1878. ^jgj^j^^^ ^y MicrOSOft® 



