448 Our Fresh-Water Planarice. 



figured by him, really exist, and are the nerve-system. At 

 page 139 of his Handbook, he says he has not been able to see 

 any commissure connecting these two ganglia in P. lactea. I 

 looked into the matter in the summer, and have since my return 

 to Oxford, on the receipt of your note, looked into it again. I 

 had written as follows for my book in the summer : speaking of 

 the c anterior ccecal end of the intestine passing up between the 

 two eyes, and underlaid in the marine genera allied to this by 

 a nervous band, passing from the ganglia in relation with the 

 eyes. According to Schmidt and Schultze [' ' Zeitschr. Wiss. 

 ZooL, x. Taf. hi. fig. 1), the same is the case in the fresh- water 

 Planarice. Of this, however, it is difficult to convince one's self, 

 with the semi-transparent species, Dendroccelum lacteum, 

 which is very closely allied to this/ On further investigation 

 I see no reason to alter this." In a subsequent letter the 

 Professor writes that " between the ccecal ends of the intestinal 

 tree-branches and the eyes, I saw a number of large cells with 

 hyaline contents and a centrally-placed granular nucleus. 

 These cells, I take it, are the nerve ganglia, loosely apposed 

 cells making up the nerve ganglia in some of the anneloids, at 

 least if we rank-Echinodermata under this head. But I saw no 

 commissure connecting these aggregations of cells." But 

 whatever may be the truth with respect to a nerve-system, the 

 Planarice are, certainly sensitive, the P. lactea particularly so ; 

 they are fidgetty under condensed light, especially when applied 

 to the head; when touched with the point of a needle, or when 

 pierced by the proboscis of one of its own kin, as by PolyeeUs 

 brunnea, the large Planaria lactea, evinces by its contortions, 

 an undoubted sensibility. Living almost exclusively in shaded 

 habitations, the Planarice cannot be expected to possess visual 

 organs of much complexity, but there seems no reason to 

 doubt that the oculiform spots, which vary from two to fifty, 

 according to the species, do in some degree perform the 

 function of eyes. 



Let us now examine the digestive system of a Planarian 

 worm. — The mouth in the true Planarice, as has been already 

 stated, lies on the ventral surface, a little below the centre of 

 the body ; it is a circular aperture, through which the 

 muscular contractile oesophagus, or tube, is protuded, whether 

 for the purpose of feeding or for defecation. In form this 

 proboscis is chiefly cylindrical, as in all the fresh-water 

 species. In the marine Leptoplana tremellaris, it is infundi- 

 buliform, and gracefully waved. The proboscis can be 

 protruded to a considerable length; according to Duges, it 

 consists of two tunics, the external one being formed of 

 longitudinal, the inner one of circular fibres, and it is to the 

 peristaltic constrictions of this inner tunic that the mechanism 



