NEMATHELMIA. 51 



The spermary is lined by nucleated protoplasm, and its cavity is 

 traversed by a cord or rachis from which mother-sperm-cells arise. 

 Each of these divides into two, and each of the halves by further 

 division produces a group of four cells (spermatocytes) which 

 divide once more. Of the eight cells thus originated four are 

 small and four large. The former are in the centre of the group 

 and constitute a sperm-blastophor, the latter are external and 

 become sperms. At first the sperms are spherical, but after 

 transfer to the female become conoidal. They never assume the 

 tadpole-shape seen in so many other cases. The basalpart of the 

 conoidal sperm is protoplasmic and nucleated, while the narrow 

 part is a highly refractive " cap " probably composed of nutritive 

 material analogous to yolk, and covered by a layer of protoplasm 

 external to which is a firm membrane. The consecutive stages 

 in sperm-development (spermatogenesis) can be easily followed 

 in a single spermary by examining its successive portions. 



Accessory male organs are present in the form of two curved 

 chitinous spicules which are contained in a pouch that opens 

 dorsally into tlie cloaca. These spicules can be protruded and 

 retracted by special muscles. 



The vesicula seminalis serves for the storage of sperms, and, 

 by the contraction of the muscular walls which it and the ejacu- 

 latory duct possess, sperms can be ejected into the vagina of the 

 female, this process being aided by the copulatory spicules. 



dorsal line (d.l) traversed by dorsal nerve (d.n), ventral line (v.l) 

 traversed by ventral nerve (v.n), and lateral line (LI) traversed by 

 excretory tube (ex) and strengthened by internal cuticular thickening ; 

 m, layer of muscle-cells, with striated part external and protoplasmic 

 part internal, the oblique lines represent processes of the latter running 

 to median lines ; i, intestine ; ov, ovary, traversed by rachis bearing 

 germ-cells ; ut, ut, uteri. F, Female Ascaris opened from ventral side, 

 and reproductive organs of left side cut short (semidiagrammatic) ; 

 ov, right ovary ; od, right oviduct ; ut, ut, uteri ; v, vagina ; i, intestine ; 

 l.l, lateral line. G, Posterior part of $ reproductive organs, longi- 

 tudinally bisected (enlarged) ; cl, cloacal opening ; ej, ejaculatory duct ; 

 sp, spicule in sac ; r, rectum. H, Stages in sperm-development (much 

 -enlarged) ; a, part of rachis, with mother-sperm-cells ; b, group of four 

 spermatocytes, surrounding a four-celled sperm-blastophor ; c, a sperm, 

 nucleus below and refractile "cap" above. K, A muscle-cell (much 

 enlarged) ; /, contractile fibrous outer part, inner protoplasmic (dotted) 

 part, with nucleus (n), and processes (pr). L, Diagram of nervous 

 system ; v.g, ventral ganglion ; l.g, lateral ganglion ; a. g, anal ganglion ; 

 l.n, lateral nerve ; d.n, dorsal nerve ; v.n, ventral nerve; co, commissural 

 nerves. 



