112 MR. F. F. LAIDLAW ON POLYCLADS [May 26, 



epithelium lies a thick basal membrane which shows no trace of 



nuclei. 



On the ventral side the muscles of the body-wall consist first of 

 a very narrow outer layer of longitudinal fibres lying against 

 the basal membrane. These are succeeded by an outer diagonal 

 layer, which in turn is followed by a few circular fibres, and these 

 by ail inner diagonal layer, the fibres in this latter running at 

 right angles to those of the outer diagonal layer. Lastly comes 

 the thick inner longitudinal layer. 



On the dorsal surface there are first a fine outer longitudinal 

 layer, next a diagonal layer, and lastly a thick circular layer. 

 Hence the dorsal muscles are somewhat similar to those of 

 Gestoidana, the ventral are more highly developed (see Lang [1], 

 t. 16. fig. 1). 



The dorsal tubercles are more muscular and broader m pro- 

 portion to their height than those of Gycloporus. ^ They are 

 covered with an epithelium, which about their base is similar to 

 that of the rest of the surface of the body, but which towards 

 their apices becomes flattened and loses its pseudorhabdites. 

 ITnder the basement-membrane, which becomes somewhat attenu- 

 ated on the tubercles, is a special layer of circular muscle-fibres. 

 In the centre of each tubercle is a small quantity of tissue richly 

 supplied with nuclei, and connected with the parenchyma of 

 the body by a strand of tissue which pierces the muscles of the 

 body- wall. This tissue is perhaps nervous in character (PI. IX. 

 fig. 6, X, y). 



The pharynx is large and much folded. The " mouth " lies 

 behind its posterior end, and communicates with the elongated 

 phaiyngeal pouch by a narrow channel. The gut-branches are 

 numerous and lie at different levels (PI. IX. fig. 6, g'). 



Genital Organs. (Plate IX. fig. 7.) 



Owing to an unfortunate accident some of the sections in the 

 region of the body where these organs occur have been lost. 

 Consequently the account given beloAv is necessarily incomplete. 



There appears to be a single genital atrium. The penis is 

 provided with a true penis-sheath (cf . Gestoplana), and there is 

 also a prostate gland. The vagina runs backwards and upwards 

 for some little distance, then bends forwards and downwards, 

 receiving on its dorsal' side the common opening of the uteri. 

 Beyond this it runs forwards and downwards towards the atrium 

 (possibly opening into it ?). 



My chief reasons for placing this oval form in the neighbour- 

 hood of Gesto2jlana are to be found in the shape of the penis, the 

 presence of a prostate gland, the backwardly- directed mouth- 

 opening, and the disposition of the eye-spots. The thickness of 

 the basement- membrane and the arrangement of the gut-branches 

 and muscles of the body- wall are, I believe, indications which 

 point in the same direction. 



