110 MR. F. F. LAIDLAW OX POLYCLADS [May 26, 



tomoses, but it is difficult to determine this owing to the great 

 accumulation of eggs in the lateral parts of the body. 



The "mouth" is about 1-5 mm. behind the anterior margin. 



The opening of the antrum masculinum is about 1 mm. behind 

 that of the " mouth." It is very minute. The small vasa deferentia 

 are full of spermatozoa ; at the level of the antrum masculinum 

 they become much contorted, and finally both open into a very 

 small median vesicle, which latter appears to open directly by a 

 minute pore into the antrum. Thus there would appear to be no 

 intromittent organ, though it is quite possible that the vesicle 

 may be to some extent everted. The vesicle is provided with a 

 veiy thin wall of circular muscle-fibres. 



The antrum femininum opens some '25 mm. behind the male 

 apei-ture ; it is small and surrounded by a number of shell-glands. 

 Dorsally it passes upwards and then backwards, receiving as it 

 tvirns back the common opening of the two uteri. Beyond these 

 it is prolonged into the very small accessory vesicle. 



The uteri extend along eithei' side of the body not far from the 

 middle line ; they vary much in diameter in different localities, 

 and in places contain spermatozoa. At intervals, where they 

 become dilated, the eggs can be seen making their way into them 

 by what appear to be simply gaps in the uteiine walls. 



The whole lateral regions are crowded with lai'ge eggs, which 

 lie embedded in a matiix that consists apparently of a yolk-like 

 material (PL IX. fig. 4). 



The female aperture is of such small size that it seems impossible 

 that the eggs can escape through it. Possibly the body of the 

 parent ruptures after a time and allows the eggs to pass out. 

 This view is suggested by the fact that in some of the sections 

 eggs can be seen lying in the gut itself. 



The genus may be defined as follows : — 



Body small, oval, and rather stout. No tentacles or sucker. 

 Body- wall muscles feeble. The pharynx of a simple type, opening 

 at the end of the first foui'th of the body. Male genital apparatus 

 of small size, copulatory organ much reduced. Female apparatus 

 simple, with a small accessory vesicle. Eyes in two rows ovei' 

 the brain. 



The position of this curious form amongst the Leptoplanida? 

 depends on negative rather than on positive characters. Its 

 exact affinities are doubtful, and it is probably a degenerate 

 organism. 



Family Cestoplanid^. 



Cestoplana filiformis, sp. nov. 



_" 15.2.01. Ribbon-shaped, about 1 in. x ^ in. Creamy white 

 with bright yellow border, and a median stripe of the same 

 colour " (cf . C. rubrocincta for colour). 



The " mouth " lies within 1-5 mm. of the hinder extremity. 



Evidently closely allied to the Mediterranean C. rubrocincta, 



