1903.] FROM ZANZIBAR AND BRITISH EAST AFRICA. 101 



Genital Organs. 



The male ajypai'atus 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 chai-actei- 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 intei-venes 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-layei- 

 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. jiellucida 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 Graff^s figures of the genital apparatus of PL pellucida 

 and PI. simrothi [3] ; also my figure of PI. armata [5]. 



Female apparatus. — The bursa copulatrix is lai"ge, and has 

 thick walls composed of an outer layer of circvilar and an inner 

 layer of diagonal radial fibres. Its walls are much folded. 

 Beyond the bursa, the vagina, which is lined with ciliated epi- 

 thelium, 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 pi-esent. 



PI. crosslandi, sp. nov. Zanzibar. 



