Fig. 100.—Male Organs, side view. T7, seventh tergum; S7, seventh sternum; Ts, DE, as before. A, B, see fig. [102]. × 8.
The testes may be found in older larvæ or adults beneath the fifth and sixth terga of the abdomen. They lie in the fat-body, from which they are not very readily distinguished. Each testis consists of 30–40 rounded vesicles attached by short tubes to the vas deferens.[169] The wall of the testis consists of a peritoneal layer and an epithelium, which is folded inwards along transverse lines. The cells of the epithelium give rise to spermatocysts,[170] which enclose sperm cells. By division of the nuclei of the sperm cells spermatozoa are formed, which have at first nucleated heads and long tails. Subsequently the enlarged heads disappear. The spermatozoa move actively. In adult males the testes undergo atrophy, but can with care be discovered in the enveloping fat-body.
The vasa deferentia are about ·25 inch in length. They pass backwards from the testes, then turn downwards on each side of the large intestine, and finally curve upwards and forwards, entering the vesiculæ seminales on their dorsal side. Each vas deferens divides once or twice into branches, which immediately reunite; in the last larval stage the termination of the passage dilates into a rounded, transparent vesicle.
The vesiculæ seminales are simple, rounded lobes in the pupa (fig. [101]), but their appearance is greatly altered in the adult by the development of two sets of utricles (modified accessory glands). The longer utricles (utriculi majores) open separately into the sides of the vesiculæ; nearer to the middle line are the shorter and more numerous utriculi breviores, which open into the fore part of the vesiculæ.
The utricles form the “mushroom-shaped gland” of Huxley, which was long described as the testis. In the adult male the utricles are usually distended with spermatozoa, and of a brilliant opaque white.
The ejaculatory duct is about ·15 inch long, and overlies the 6th-9th sterna. It is wide in front, where it receives the paired outlets of the vesiculæ seminales. Further back it narrows, and widens again near to its outlet, which we find to be between the external chitinous parts, and not into the penis, as described by Brehm. The duct possesses a muscular wall for the forcible ejection of its contents, and in accordance with its origin as a folding-in of the outer surface, it is provided with a chitinous lining. In the adult the fore part of the duct may be distended with spermatozoa.
The ejaculatory duct is originally double (p. [194]), and its internal cavity is still subdivided in the last larval stage or so-called “pupa.”