4 ARKIV FÖR ZOOLOGI. BAND 14. N:0 18. 



fensive weapons for this polyclad. In accordance with that 

 they occur almost exclusiveJy on the dorsal and lateral parts 

 of the body. There they can be seen with their intact styletis 

 protruding out of the epithelium. A lot of empty capsules 

 show that some of them also have functioned. Their great 

 number indicates that they must be of value for the pro- 

 tection of the animal. In a single transverse section, 5 (x 

 thick, I counted more than fifty capsules. This will give a 

 very considerable number for the whole animal. 



Behind the frontal line there is, as always in the poly- 

 clads, an epithelial transverse sensory furrow^ and in con- 

 neotion with it there is an unusually large mäss of subder- 

 mal mucuous glands which fill up the anterior end of the 

 body. Beside this transverse furrow this polyclad po?sesses 

 a peculiar and unique epithelial furrow (Plate II, fig. 1), 

 running on each side in the length direction of the body 

 but only in the anterior half of it. This furrow is strictly 

 marginal, having rather a dorsal position on the very thick 

 margin. As in the transverse furrow, the deepening of it is 

 formed by the cells being much lower — less than half — 

 than the ordinary epithelial cells. The most characteristic 

 feature of the furrow is the presence of epithelial mucous 

 gland cells of a special kind. They are columnar, not sac- 

 like as such cyanophilous cells usually are. The secretion is 

 stained more deeply than common mucous glands, resembling 

 in this respect the glands of the frontal sensory organ of 

 certain other turbellarians (some alloeocoels) and nemerteans. 

 It is tempting to assume that these marginal furrows have a 

 sensorial function and the occurrence of these special gland 

 cells makes it probable that this may be similar to that of 

 the frontal organ and cephalic organs of the nemerteans, i. e. 

 an organ of smell or rather a chemical sense organ. The 

 gland cells occur in a row consisting of two cells in breadth 

 on the ventral side of the furrow, guarding in this way the 

 entrance to the furrow. The preservation was not good 

 enough to allow more detailed researches on the sensorial 

 cells. 



The colour of the animal is caused by the presence of 

 brown pigment granules in the dorsal epithelium and be- 

 neath it. As Chromoplana lives in tidal pools much exposed 

 to the sun this dense and dark pigment must be of value 



