DESICCATION IN PHILODINA ROSEOLA. 351 



Dorsally, and arising at the posterior margin of the head, is 

 the tactile organ (PI. I., Fig. i, t. 0.) which shows from two to 

 four segments according to its state of extension. It is capped 

 at the end by a tuft of short cilia. Nerve fibers connect it with 

 the brain as Zelinka has shown. 



The brain (Fig. i, or.) lies with its anterior margin just at the 

 base of the tactile organ, while it extends posteriorly slightly 

 over the forward part of the mastax. It is triangular in shape 

 with the sharpest angle extending forward. The eyes (Fig. i , e) 

 which are red in color, lie dorsal to the brain. 



The excretory canals (Fig. 2, e. c.} extend into the head and a 

 terminal flame cell (/. c.) can sometimes be seen beating at the 

 base of each trochal disc. These flame cells are perhaps best 

 seen when the trochal discs are folded in. They appear very 

 close to the margins of the folded discs (PI. II., Fig. 3). 



The trunk is almost entirely filled with the organs of digestion 

 and those of reproduction. In its most anterior part the mastax 

 (PI. I., Fig. i, m) is prominent. Food enters this by way of 

 the narrow, ciliated pharanyx (PI. I., Fig. 2, ph.}. The mastax 

 proper consists of two more or less crescent-shaped jaws. Trans- 

 verse ridges, which at the inner margins continue as short pro- 

 jections, form the teeth (PI. I., Fig. i, t). In all the animals I 

 have studied there have been two teeth on each jaw. A few 

 authors report cases where there are three teeth on one jaw and 

 two on the other. 



The mastax is surrounded by glands which probably contrib- 

 ute a digestive fluid to the food as it is being crushed in the 

 mastax. There are five of these salivary glands, two of which 

 lie clorsally and three ventrally. The dorsal ones (Fig. i, 5. g.) 

 follow the outline of the mastax quite closely, while those on the 

 ventral side are usually larger and extend posteriorly (Fig. 2, 5. g.). 

 In the living animal these glands show a granular cytoplasm with 

 nuclei of varying sizes. These nuclei appear as bright spots 

 against the darker cytoplasmic background. 



From the mastax a narrow esophagus leads to the stomach- 

 intestine (PI. I., Fig. i, st. I.}. In most cases it is difficult to 

 see the esophagus in the living animal. This is also true of a 

 pair of glands which lie at the anterior end of the stomach- 



