51] LIFE HISTOR Y OF TREMA TODES—FA UST 51 



change that has taken place in the ventral portion of the system. Here the 

 space between the ventrales has become exceptionally wide and a prominent 

 commissure has grown out from the trunks, commonly known as the subesopha- 

 geal commissure. It is the homolog of the transverse commissure occuring 

 along the entire ventral side. The intermedins trunk has become fused with 

 the posterior lateralis, in part, and then crosses over to the ventralis. This 

 is the connection known in adult nerve anatomy as the ventrolateral com- 

 missure, a strong and important intercommunicating trunk (Fig. 123). In 

 the developmental stages no trace of palatinus or pharyngealis has been found. 



Cercaria glandulosa, a xiphidiocercaria, is favorable material for the study 

 of the minute structure of the nerve fibers and endings. In the anterior 

 end of this larva there occur in five frontal sections of 8/i thickness all of the 

 fundamental nerve endings of this region. In section 1 of the worm (the 

 most dorsal section), there are no nerve structures save a few sensillae to the 

 dorsal lip of the oral sucker. They receive innervation from the anterior 

 dorsalis, and derive that innervation from the anteriormost fibers seen beneath 

 in section 2, just in front of the musculuspreoralis. Section 2 (Fig. 68) shows 

 the trunk of the dorsalis descending into the oral musculature. It has three 

 main branches, one coursing to the preoral region to supply the conductive 

 strands for the preoral sensory endings, one becoming the short superficalis, 

 and a longer one, the profundus, passing under the endings of the superficialis. 

 In the region of the musculus preoralis, the apical sensory field is continuous 

 across the sucker from right to left. In section 3 (Fig. 69) are illustrated the 

 main outlines of the central nervous sytem, together with the anterior trunks. 

 Here is the dorsal portion of the gangUon cells. Anterior and dorsal is the 

 dorsal commissure and ventral is the subesophageal commissure. The for- 

 ward traces are the trunks of the laterales with the outermost superficial ramus 

 palpalis and the more deeply situated ramus muscularis. The latter branch 

 innervates the musculus preoralis and the anterior lip of the oral sucker. On 

 the left is the trunk of the anterior ventraHs, arising from below the mass 

 of the ganglion cells. At the anterior extremity is the apical sensory field. 

 The dorsolateral commissure is very clearly shown in this section. Section 4 

 (Fig. 70) shows the remainder of the central gangUa with the left anterior 

 ventralis passing forward. This is a large trunk, with an especially important 

 ramus palpalis leading to the apical sensory field, and a small oral nervus 

 communicans supplying the oral nerve ring. This ring completely encircles 

 the superficial region of the oral sucker and connects with the superficial 

 branch of the dorsahs. The ramus muscularis of the ventralis and the palatine 

 branch of the ventraHs are found in section 5 (not figured). 



Passing caudad all the posterior roots are well defined. Four posterior 

 roots are visible in section 3 (Fig. 69). These include the posterior dorsales, 

 laterales, ventrales, and pharyngeals. In a fortunately cut section of the 

 same species the innervation of the acetabulum is beautifully demonstrated 

 (Fig. 71). The two main longitudinal trunks, the ventrales and the laterales, 



