SENSE ORGANS OF AMIURUS. 353 



therefore devoted to the origin and distribution of the trigeminus 

 group and to the auditory apparatus. The following order is observed 

 in the description of the various parts : — 



I. Central nervous system. 

 II. Peripheral nervous system. 

 III. Sense organs. 



I. CENTRAL NKRVOUS SYSTEM. 

 A.— THE BRAIN. 



As in most other Teleosts the cranial cavity of Amiurus is by no 

 means filled up by the brain, which is surrounded by a large quan- 

 tity of areolar connective tissue rich in vessels and fat. This tissue is 

 continued backwards into the neural canal and into the cavities in 

 which the semicircular canals are lodged, to which, and indeed to the 

 whole auditory labyrinth, the tissue acts as ' perilymph.' 



The recent observations of Mayser 1 and Kabl-Riickhard 2 have con- 

 firmed Stieda's interpretation of the various parts of the Teleost 

 brain, and are thus entirely opposed to the views expressed by 

 Fritsch in his " Untersuchungen fiber den feineren Bau des Fisch- 

 gehirns." As was to be expected from the affinity of the Siluroids 

 to the Cyprinoids, I have found Mayser's researches, which are 

 chiefly based on the latter group, of the greatest service in studying 

 the brain of Amiurux. The points in which that genus differs from 

 Gyprinus I shall call attention to in the course of my description 

 My obseiwations have, however, not been extended to the study of 

 the finer structure of the brain, and the sections figured are rather 

 intended to complete the topographical description than to furnish an 

 exhaustive account of the nerve-fibre tracts. 



Owing to the abundant perilymphatic tissue it is easy to remove 

 the roof of the brain case without injuring the brain. The appear- 

 ance of the organ when so exposed is represented in Fig. 13, PI. I. 

 In front we have the so-called cerebral hemispheres (GB) which after 

 the brain has been hardened appear to be two solid masses separated 

 by a longitudinal medial groove, but which in the recent condition 

 are seen to be two oval thickenings in the floor of a sac whose roof 

 and walls are extremely thin and transparent, and whose cavity is the 

 ventriculus communis of the secondary forebrain, prosencephalon. In 

 comparison with many other Teleostean forms the cerebral hemis- 

 pheres of Ainiurus are of large size. From the ventral surface of 



] Zeit. wiss. Zool. XXXVI. 2 Arch. Anat. Pliys. 1882-3. 



