On the reproductive system of Planaria simplissima. 453 



there is no sharp transition between the epithelium of the seminal 

 vesicles and that of the penis lumen the latter is somewhat columnar, 

 shows the cell outline and seems to resemble more the epithehum of 

 the atrium. The musculature is shown on PI. 31, Fig. 3, where a 

 sector of the penis and atrium in cross section are represented in their 

 relation to the dorsal wall of the animal. Just beneath the outer 

 epithelium is a strong circular layer (cmja) and following this a very 

 much weaker system of scattered longitudinal fibres hnp). Both are 

 continuous at the base of the penis with similar layers investing the 

 atrial cavity (acm and aim) and the outer is continuous at the free 

 end of the penis with the circular layer around the lumen (cl). This 

 circular layer of the lumen is at places found gathered up into 

 bundles that run out as radial muscles (ra). The musculature 

 of the penis is therefore built from the two layers of the atrial 

 cavity. The same two layers are continued into a strong muscu- 

 lature for the vagina, from which they follow the uterus as a more 

 delicate investment (PL 31, Fig. 3 um), but do not extend to the 

 oviducts. 



The atrial chamber (PI. 31, Figs. 1 and 8 at) is lined with 

 cuboidal epithelium resting on a delicate basement membrane, beneath 

 which are the circular and longitudinal muscle systems just mentioned 

 (PL 31, Fig. 3). The genital pore (PL 31, Fig. 8 o^O connecting the 

 chamber to the outside is a canal of some length surrounded at its 

 ventral end by a sphincter muscle formed from the fibres of the trans- 

 verse and diagonal layers of the sub-dermal musculature. Radial 

 fibres are present along its length and the strong circular fibres of 

 the sphincter are continuous with the corresponding layer of the atrium. 

 The rhabdites disappear at the mouth of the pore and the epithelium 

 of the chamber shows no corresponding structure. The only other 

 opening to the atrium that of the vagina (va) will be described with 

 the female organs. 



The female reproductive system consisting of ovaries, oviducts, 

 vitellaria, uterus and a vagina with its shell-gland is best seen in the 

 reconstruction shown on PL 31, Fig. 1. 



The ovaries are irregularly lobed masses situated just inside and 

 above the longitudinal nerve-trunks and directly under or behind the 

 fourth gut-lobe of either side. They are not always compact and 

 frequently consist of straggling lobes irregularly connected with each 

 other and with the head of the oviduct. This condition reaches an 

 extreme when a short distance behind the ovary proper similar masses 



