OCR Text |
Show 1903.] FROM ZANZIBAR AND BRITISH EAST AFRICA. 101 Genital Organs. The male apparatus consists of a short, muscular, somewhat barrel-shaped penis, which tapers a little towards its free posterior end, where it carries three large chitinous hook-like structures, identical in character with those found in PI. armata. In front of these its entire lumen is lined with the small, very numerous chitinous spines so characteristic of this and allied genera. The penis-muscles are longitudinal and diagonal. The prostate gland is large, and, with the penis, is enclosed in an outer muscular-sheath, the walls of which are made up of an inner circular and an outer longitudinal layer of muscle-fibres. At the distal end of the penis the prostatic muscles come into close contact with the muscles of that organ, but at the upper end of the penis a wide space intervenes between it and the sheath. Here the muscles of the penis are collected into bundles of retractor fibres, and traverse the surrounding sheath-cavity to join the muscles of the sheath. The prostate is closely enfolded by the inner muscle-layer of the sheath ; it gives off a short duct which enters the base of the penis after receiving the ductus ejaculatorius from the vesicula seminalis. As in PI. pellucida and PI. armata, this duct runs for a short distance right inside the prostatic duct. The vesicula seminalis lies outside the sheath. The vasa deferentia are much dilated. The antrum masculinum, into which the free end of the penis projects, is lined with a ciliated non-secretory epithelium. Cf. von Graffs figures of the genital apparatus of PI. pellucida and PI. simrothi [3] ; also m y figure of PI. armata [5]. Female apparatus.--The bursa copulatrix is large, and has thick walls composed of an outer layer of circular and an inner-layer of diagonal radial fibres. Its walls are much folded. Beyond the bursa, the vagina, which is lined with cdiated epithelium, runs forwards and upwards through the large shell-glands, and then turns sharply back, receiving as it does so the common duct from the uteri. Beyond this it is continued back as the thread-like accessory vesicle, which ends blindly. The walls of the bursa show no trace of secretory activity. The following is a list of species which can be referred at present with tolerable certainty to the genus Planocera:-- A. Species in which the penis is armed with large chitinous hooks as well as with spines. a. Six hooks present. PI. armata Laidlaw [5]. Maldives. b. Three hooks present. PI. crosslandi, sp. nov. Zanzibar. |