(b) Male Sexual Organs.—There is never more than one testis (fig. 266), which is a straight or sinuous tube of the same construction as an ovary, and in which the mother cells originate in the same manner as the ova. In the same way as the ovary passes into the uterus, so does the testis pass into the spermatic duct; the latter is often divided into the somewhat dilated seminal vesicle and into the muscular ductus ejaculatorius, which, running ventral to the intestine backward (fig. 267), finally opens into the cloaca. In many species, e.g., A. duodenale, the ejaculatory duct is surrounded for a greater or less portion of its extent by the cement gland, the secretion of which (brownish or blackish in colour) serves for copulation. The ejaculatory duct of the large Ascaridæ is for the most of its course surrounded by a muscular network which takes its origin from the two dilator cells of the gut (fig. 268 F.). The spermatozoa of the Nematodes, it may be noted, only attain their full development after the sperm mother cells have been conveyed by copulation into the uteri of the female genitalia. In their form (sheathless, capable of amœboid motion) they differ from those of most other animals.
Spicules.—The male genital apparatus is also provided with one or two sacs, situated on the dorsal side of the intestine, and opening into the cloaca. In each sac there is a chitinous rod-like body, the spicule. Further, in many cases there exists, more or less fixed in the dorsal wall of the cloaca, a chitinous structure, the accessory piece or gubernaculum, the latter name implying its function of guiding the spicules during copulation (fig. 264A). A special muscular apparatus, consisting of protractors and retractors, moves the spicules. The protractors or exsertors in the large Ascaridæ consist of four flat band-like muscles which surround the spicule sac. Two long muscle cells which arise proportionally far forward on the dorsal side of the lateral line and are inserted into the base of the spicules serve as retractors. The spicules can be projected from the cloacal orifice (anus) during copulation, and when they are introduced into the vagina they serve as prehensile organs, perhaps also as stimulatory organs.
Fig. 266.—Male of the rhabditic form of Angiostomum nigrovenosum. A., anus; I., mid-gut; T., testicular tube; O., oral orifice; P., papillæ; Sp., spicule. Magnified.
Fig. 267.—Transverse section through the posterior extremity of the body of Ascaris lumbricoides (male). The intestine is in the middle, and the lateral lines are subjoined thereto; above the intestine the two spicule sacs are seen; below is the ductus ejaculatorius. The muscular fibres are between the lateral and median lines. Magnified.
Bursa copulatrix.—The males in many genera possess epidermal wing-like appendages at their posterior extremity. These are supported by elongated tactile papillæ called ribs. In the most highly developed bursæ, e.g., in the Strongylidæ, the ribs are called rays, as they consist not only of nerve fibres but mainly of “pulp,” i.e., prolongations of the subcuticular layer. Bursæ are either open, i.e., bilaterally symmetrical, or closed, when the posterior border is continuous all round. A pseudo-bursa is one unsupported by ribs or rays, e.g., in Trichuris. The bursa serves as an organ of prehension during copulation. Some forms, moreover, carry a sucker at the posterior extremity (e.g., Heterakis); in others the spicules and other prehensile organs are absent; they are then replaced by an evertible cloaca, e.g., Trichinella.