MUSEUM OF COMPARATIVE ZOOLOGY. 27 



seen more than a few loops in the head region, and these were seen only 

 when the animal was put under great pressure, resulting in disintegra- 

 tion of the tissues. 



The nervous system of Phagocata agrees in the main with the descrip- 

 tions given by Lang ('81, p. 53) and lijima ('87, p. 349) for other plana- 

 rians. The longitudinal nerve trunks unite near the anterior end of the 

 body in a well developed brain mass (Plate III. Figs. 25 and 33), and 

 posteriorly are connected with one another by fine commissures. Larger 

 commissures unite the trunks to one another throughout their whole 

 length, either running straight from trunk to trunk, or branching in 

 their passage (Plate IV. Fig. 38). The latter condition may be regarded 

 as closely related to one in which two commissures are united to each 

 other by means of a connective, a condition that often occurs. There 

 is no fixed relation between the number of transverse commissures and 

 the lateral diverticulee of the intestine, but lateral nerves are usually 

 given off from the main stems at points opposite to the union of the 

 latter with transverse commissures (Plate IV. Fig. 38). The main nerve 

 trunks are prolonged anterior to the brain. They diminish rapidly in 

 size, and give off several lateral branches, which are directed obliquely 

 forwards and outwards (Plate III. Figs. 25 and 36), and they finally 

 break up into minute branches which form a network. The lateral 

 nerves from the main trunks run, sometimes with, sometimes without 

 branching, to the margins, where they unite with a second pair of finer 

 longitudinal nerves, — the marginal or peripheral nerves (Plate IV. 

 Fig. 37, n. pi'ph.). The marginal nerves form the lateral edges of a 

 great nervous network, which lies near the ventral surface just inside the 

 sheet of longitudinal muscles. Figures 37 and 38 represent portions of 

 two successive horizontal sections close to the ventral surface. The 

 sections are 30 /x thick, and pass through the floor of the pharyngeal 

 chamber ; the light areas show where the knife has cut through the wall 

 into the pharyngeal cavity. The animal having been sectioned from 

 the ventral side, Figure 38 is the deeper (i. e. more dorsal) section. 

 The position of the oral opening (o) indicates that the portions of the 

 sections shown are from the same region of the body. In Figure 38 are 

 seen the main nerve trunks (n. Vp.) together with transverse commis- 

 sures {com. f.) and lateral nerves (?i. L). It may be seen from Figure 37 

 how the median branches from the peripheral nerves (n. pi'ph.) break up 

 into a network or plexus, which is distributed to the muscles (plx. mu.). 

 This network covers the whole of the ventral surface, and at the extreme 

 anterior end of the body is continuous with finer ramifications of the 



