SARGENT: THE OPTIC REFLEX APPARATUS OF VERTEBRATES. 215 



tlie tectum. It is through these tracts that the apparatus is put in 

 direct connection witli the endings of the optic nerve-fibres. 



In Tautoga onitis, a much larger species than the preceding, but 

 closely related to it, the apparatus is without essential differences. 

 Reissner's fibre within the canal is from 4 to 5 micra in diameter, the 

 lumen of the canal being 25 micra in diameter. 



Balistidae (169). In young Balistes vetula, 2 cm. long, the torus 

 is short and not well developed. The ependymal cells of the torus are 

 prominent, and the nerve-cells relatively few. The axons of the median 

 ventral torus-cells pass into the fissure between the torus-lobes in 

 numerous fine trunks, and behind the posterior commissure unite with 

 the trunks which enter the ventricle through the ' Schaltstuck.' Reiss- 

 ner's fibre is a delicate thread 1 micron in diameter. 



MoNACANTHiDAE (170). In a young specimen of Alutera schoepfii 12 

 cm. long the torus was somewhat better developed than in Balistes. 

 Six to eight delicate fibre-like trunks emerge from the ' Schaltstilck ' 

 and running parallel gradually unite (Plate 7, Fig. 49). Even under 

 the valvula, however, several parallel trunks were found {fas. Reis.). 

 These unite beneath the cerebellum to form Keissner's fibre, whose 

 diameter is from 1.5 to 2 micra. 



CoTTiDAE (179). Both young larvae and adults of the sculpin, Myoxo- 

 cephalus aeneus, have been studied. In larva 15 mm. long Reissner's 

 fibre in the rhomboidal fissure measures 1 micron in diameter. In the 

 adult it has a diameter of 6 micra. It is formed from one chief trunk 

 emerging from the ' Schaltstuck ' under the posterior commissure, and a 

 number of small trunks which enter the mesocoele above the posterior 

 commissure, in the fissure between the lobes of the torus. All these 

 unite and fuse immediately behind the commissure. 



Cyclopteridae (182). In the one adult Cyclopterus lumpus studied, 

 the torus was but little developed. Numerous fine fibre-like trunks 

 emerging into the ventricle in the median plane from the whole length 

 of the 'Schaltstilck' unite immediately to form Reissner's fibre, whose 

 diameter is 3 micra. Some of these trunks come from so far forward 

 that it is unlikely that they have their origin in the torus, but rather in 

 the ganglia habenulae. 



Triglibae (184). In the two specimens of the sea-robin, Prionotus 

 strigatus, examined, Reissner's fibre measures, respectively, 2.5 and 3.5 

 micra in diameter. The fibre enters the ventricle as a whole just an- 

 terior to the posterior commissure. 



Malacanthidab (190). In the tilefish, Lopholatilus chamaeleonticeps, 



