NEMATODA. 68 1 



vesicula seminalis, and ductus ejaculatorius. The walls of the whole tube 

 are composed of a delicate membrane, lined in the testis and vas deferens 

 by protoplasm containing nuclei, and disposed in lines which are longitu- 

 dinal, and in the testis parallel, in the vas deferens interlaced, whereas the 

 vesicula seminalis and ductus ejaculatorius have a distinct epithelium very 

 variable in character in different genera and species. In the vesicula each 

 cell is in some of the larger species, e. g. A. megalocephala, provided with 

 filamentous processes capable of changing their shape. The ductus ejacu- 

 latorius has a well-formed external layer of muscles, chiefly transverse. 

 Properly speaking, the vesicula is only its upper and less muscular part. 

 Two caeca of unknown function open into the male duct near its termina- 

 tion in Pleterakis and Pelodera. The spermatozoa are peculiar. During 

 their formation they are attached to a central, or in Trichina, Trichocephalus, 

 and Trichosomiim lateral, rhachis, which may become much divided, but 

 they do not attain their characteristic shape until transferred to the female. 

 In the male organ they are small truncate nucleated spheres. Four types 

 of form and structure have been distinguished by E. van Beneden succes- 

 sively assumed in the uterus : (i) spheroidal a layer of homogeneous 

 substance covers one pole of the sphere ; (2) pyriform this substance 

 assumes a conical shape ; (3) campanuliform the substance becomes a 

 cornucopia-like figure, and is separated at its base from the protoplasm 

 of the body of the spermatozoon by a limiting plate, from which a 

 clearly defined line rises and traverses the cornucopia ; (4) conoid the 

 cornucopia-figure is replaced by a cone, which consists of a superficial 

 membrane, a layer of protoplasm, and an axial refractile rod. One of the 

 forms 2, 3, or 4, may effect impregnation. The protoplasmic body of the 

 spermatozoon is capable of amoeboid motion a . Copulatory organs take 

 the form of spicules, and a ' bursa.' Spicules are wanting in Sphaerularia, 

 Trichina, Dermatoxys. One is present in Oxyuris, Trichocephalus, and 

 Trichosoma ; two dissimilar in Heterakis, Filaria. &c. ; two similar in all 

 respects in the majority of genera 2 . The spiculum is chitinoid, pointed, 

 often dark-coloured, and either homogeneous or containing a soft core- 

 It is contained in a sheath, which is an evagination of the dorsal wall of 

 the cloacal region of the rectum, and with which its base is continuous. 

 The sheath has a smooth internal surface except in most species of Tri- 

 chocephalus, and in Trichosoma aerophilium, where it is covered with spinules. 

 It is provided with retractor and exsertor muscles, and may, as in Tricho- 

 cephalus, be partially extrusible. A bursa is not always present. In its 



1 This motion has been actually observed, but not in Nematoda inhabiting warm-blooded 

 Vertebrata. It is possible that in such cases the sperm is motile only at the natural temperature of 

 the host. E. van Beneden draws attention to their great variability of outline in specimens pre- 

 served in Osmic acid. 



* The two spicules are occasionally fused at their apices, and their bases supported by an extra 

 piece, e. g. in Angiostomum. 



