MUSEUM OF COMPARATIVE ZOOLOGY. 167 



encloses the oesophageal cell, so that no space is left on any side. The 

 dorsal line does not extend as far forward as the partition, hut the ventral 

 line, which takes its origin from the brain, passes under the partition, 

 the fibres of which spread out above it. 



The anterior wall of the chamber is grooved externally, and this median 

 groove, already mentioned, is supplied with one, or often two, low papillar 

 elevations on each side. The cuticula on the anterior face of the head has 

 about twice the thickness of that over the body in general. The underly- 

 ing hypodermis from the mouth opening upward over the anterior dorsal 

 aspect of the head is composed of high narrow cells, which are contin- 

 ued basally into one or more processes that are probably connected with 

 nerve fibres. These relations are represented in Figure 92 (Plate VII.), 

 which shows a somewhat oblique section near the apex of the head. 

 It is the dorsal and lateral cells that are in question, and they show in 

 some places very clearly the basal processes. Two such cells more 

 highly enlarged are shown in Figure 93. The fibrous masses on either 

 side into which the processes pass are the anterior prolongations of the 

 fibrous mass of the brain. Burger ('91, p. 637) has described these 

 cells as rounded at the deep end, and he did not find their connection 

 with the nervous system. 



Along this part of the head and farther ventrad on the anterior face 

 minute pore canals in the cuticula are by no means uncommon, and 

 once or twice in total preparations fine hairs were seen in this region. 

 Without having demonstrated any connection between the canals and 

 hairs, I believe they are really united, and that the mass of cells which 

 is here connected with the brain is sensory in function. Just dorsad 

 to the mouth opening there was found in three specimens a small per- 

 fectly regular cuticular pocket about 30 n in diameter. Its nature and 

 value could not be determined, but, if at all significant, it is probably 

 the remnant of a larval organ. 



The striking transparency of this region in the living animal is due to 

 the thinness of its walls. Everywhere but at the extreme anterior end 

 the cuticula is thin, and, although the muscular layer begins in this 

 region, it is insignificant. Only on the ventral surface does one find a 

 mass of tissue, the brain with its capsule. The dark streak which in 

 the living animal crosses the anterior chamber just in and above this 

 mass is the oesophagus already described. The chamber is filled with a 

 fluid in which float small scattered corpuscles of great transparencv. 

 Two such are shown in Figure 95, immediately below the ganglionic 

 cell, cL gn. V. 



