286 F. F. LAIDLAW. 



seminalis lies outside the outer sheath. It is small, with thick muscular walls composed of 

 circular fibres. The vasa deferentia before joining it are. much swollen and full of spermatozoa; 

 they are lined with a cubical ciliated epithelium, and have no nuclei. The vesicula itself 

 contains no spermatozoa. 



2. Planocera langii, sp. n. (PI. XIV. fig. 1, and PI. XV. fig. 13). 



One specimen fi-om Minikoi. " White transparent form." Body flat, oval ; margin folded. 



Total length about 20 mm. Front margin to mouth opening 11 mm. Front margin to 

 male aperture 13'5 mm. Male to female aperture about "3 mm. Tentacles about 7 mm. fi-om 

 the anterior margin, and about 1'5 mm. apart. 



Tentacular eyes numerous, small, lying at the base of either tentacle in a dense cluster. 

 Tentacles slightly bilobed at their ends. Behind the tentacles is a single pair of small eyes, 

 lying over the brain. Colour white, with a few small black chromatophores lying scattered 

 round the pharynx region dorsally. There are in addition a number of exceedingly small black 

 spots consisting apparently of pigment granules \'isible on the dorsal surface above the hinder 

 part of the pharynx. These granules lie in the parenchyma, and are not of course comparable 

 in any way to the diverticula described in the previous species. Similar granules occur in an 

 undescribed species of Planocera from Rotuma. 



Genital apparatus. Aii examination of the accompanying Figure 62 shows that the 

 present species differs strikingly so far as 

 these organs are concerned fi:om PL armata. ^c 



In fact it seems impossible to homologize 

 the bursa copulatrix of the one with that of 

 the other. The female aperture (?) leads 

 into a spacious antrum femininum into which 

 the shell-glands (sh.gl.) open. From the an- 

 trum a short passage runs dorsalwards. It 9 sJ^~ 

 quickly divides to form the vagina which ^ „, „ , 



'■ •' . I'lG. 62. Female apparatus of P/anocera toj^u (diagrammatic). 



runs backwards, and the bursa copulatrix For explanation of lettering see text. 



(6. c.) which extends forwards alongside the 



penis, lying at rather a higher level than the vagina (see fig. 13). The latter after a 

 short distance bends ventralwards, and at the same time receives the separate openings of 

 the uteri (ut). Beyond this the character of its lining epithelium alters completely, and the 

 organ is continued backwards as an elongated vesicle, which may be called the receptaculum 

 seminis (?■. s.), homologous with the accessory vesicle of PL armata. A remarkable feature of 

 the male apparatus is the presence of a pair of vesiculae seminales, dilations of the terminal 

 parts of the vasa deferentia with thick muscular walls. Compared with PL armata, this species 

 has a long ' outer sheath ' with feeble walls. The penis is long and twisted, without retractor 

 muscles. The chitinous spines lining its lumen are relatively few, and there are neither chi- 

 tinous hooks nor ring. The penis extends right back to the level of the prostate, which com- 

 municates with it by a short wide duct. 



Female organs. The receptaculum seminis (= accessory vesicle) is lined by a regular, 

 columnar, ciliated epithelium, resting on a fine, basal membrane. All the nuclei lie at the lower 

 extremity of their cells, close to the membrane. They have a lightly staining ground-substance 

 with scattered chromatin granules. The protoplasm is faintly granular. The receptaculum lies 



