48 ILLINOIS BIOLOGICAL MONOGRAPHS [48 



made out the ganglion cells of the pharynx region and recorded their ob- 

 servations on the nuclei. Bettendorf (1897), working on Fasciola hepatica 

 with intra vitam methylene blue and Golgi methods, has brought out clearly 

 and convincingly the nervous sytem of this worm. This study has been aug- 

 mented by the work of Zailer (1914). 



In view of the extensive study of the nervous system of the adult tre- 

 matode, it is a matter of no little surprise that so little has been done on the 

 nervous structure of the cercaria and the parthenita. Looss (1894:245) has 

 confessed the difEculty in making such a study and had observed that "ein, 

 wie es scheint, nicht unbetrachthcher Theil derselben fallt in die Zeit der 

 Cercarienentwicklung, und weiterhin, ist auch der ganze Apparat wahrend 

 seiner Ausbildungzeit, dass es mitunter recht schwer ist, zu entscheiden was 

 zu ihm und was zu dem umgebenden Parenchyme gehort. " However, Looss 

 depended on living mounts for his study and did not use preserved material 

 or avail himself of intra vitam methylene blue technic. By the use of an 

 eosin counterstain against a hematoxylin background the writer has been 

 able to secure remarkably clear sections showing with extraordinary delicacy 

 the nerve branches as well as the central nervous system. It is the purpose 

 of this section of trematode morphology to present data and observations 

 on the development and structure of the nervous system in parthenita and 

 cercaria. 



The central nervous system of the adult trematode consists of two central 

 ganglion masses, situated dorsal and lateral to the pharynx and yoked together 

 by a transverse commissure passing dorsal to the pharynx. The appearance 

 of this structure has been aptly described by Lang (1880:46) as a saddle 

 between oral sucker and pharynx. In cross section it is lunar. Here are 

 centered the most of the ganglion cells, altho they are frequently found poster- 

 iorly, and often in the sensory apparatus of the oral and ventral suckers. The 

 system also has a subesophageal commissure which differs in size and shape in 

 different species of flukes. Extending forward into the region of the oral 

 sucker are three pairs of nerve trunks, the dorsalis, lateralis, and ventralis. 

 Of these three the latter is the most fully developed. It has a ramus muscular- 

 is which is both motor and sensory (Zailer), and an extensive connection with 

 the oral nerve ring. The anterior lateraUs is also a strongly developed trunk, 

 with a ramus muscularis and a ramus palpalis, and transverse commissures 

 to the anterior dorsalis and posterior lateralis. The anterior dorsalis is a 

 weakly developed nerve which innervates the apical sensory field. A trans- 

 verse commissure connects the two dorsales above the head muscle sheath. 

 In addition to these three primary trunks, the palatinus, a weak motor nerve, 

 lies internal to the anterior ventralis. Posterior to the central nervous system 

 are the three posterior trunks, the dorsalis, lateralis, and ventralis. The ven- 

 tral trunk is by far the most strongly developed. In addition to these is the 

 small but conspicuous internal branch of the ventralis known as the pharyn- 

 gealis. It occupies a posterior position, corresponding to the palatinus anter- 

 ior to the central nervous system. 



