THE CRANIAL NEEVES AND LATERAL SENSE ORGANS OF FISHES. 203 



(1897, 90) *. In his later work (1897, 6, p. 625) Allis states, what I had previously- 

 suggested, that the so-called lateral line branch of the IXth of Amia is really a branch 

 of the lateralis lateral line nerve. 



A rather curious mistake is made by Ayers (1892, 7), who describes the lateralis 

 latei-al line nerve as the "anterior (dorsal) branch of the IXth." Pollard makes a 

 statement which 1 had overlooked in my previous work, and which is closely paralleled 

 by the condition sometimes found in Chimcera {46, p. 616). He says (1892, 160, p. 395) 

 " In a young specimen of Poli/ptents about 20 cm. long, which was cut into sections' 

 there appeared to be a commissure from the ganglion of the trigeminus to the 

 ophthalmicus superficialis of the facial. The material was, however, not well preserved, 

 and consequently the existence of this commissure -which would represent the superficial 

 portion of the trigeminus could not be determined with absolute certainty." The buccal 

 and superficial oplithalmic lateral line nerves of Polypterus arise from a common trunk, 

 and the former accompanies the superior maxillary division of the Vth. Miss Piatt 

 (1896, 158) describes the IXth nerve of Necturiis innervating sense organs of the lateral 

 line, and considers the operculo-mandibular line of organs to be composed of two distinct 

 portions. Kingsbury (1897, 114) states that the lobi trigemini of Elasmobranchs and 

 Ganoids are directly homologous and constitute the lateral line centre, but that in 

 Teleosts tiie lobus trigeminus is another structure and belongs to the fasciculus communis 

 system. I had originally intended writing a section on the function of the lateral line 

 system, but this must be deferred for the present. In the meantime I may refer those 

 interested in the question to the works of Ayers (1892, 7), Dercum (1880, 59), Eritsch 

 (1888,76, and 1890, 77), Fuchs (1895, 78), de Sede (1885, 129), Ilichard (1896, 167), 

 Savi (184.4, 178), Stahr (1897, 196), (Willey 1891, 223), and Ramsay Wright (1884, 227). 



Summary. 



1 . The present communication contains the first description of the lateral sense organs 

 and their nerves in the genus Gadus. 



2. The sensory canal system of Fishes, both recent and fossil, is resolvable into a 

 common type, to which the lateral canals of all forms can be reduced. This type 

 includes a lateral canal on the body, a canal over the eye, another underneath it, and 

 finally one related to the lower jaw. All these canals may be connected by median 

 commissures with their fellows of the opposite side. 



3. The sensory canals of Gadus may be described as having diverged but slightly from 

 the typical form. The canal sense organs are somewliat reduced in number, which 

 involves a similar reduction in the dermal tubules. There are no Savian vesicles or 

 Lorenzini's ampuUse, but pit organs of the usual constitution are fairly common. 



4. The lateral line systems ofGadusmorrhua and Gadus vii^ens exhibit specific differences. 



5. The sensory canals, by their skeletal support, become secondarily related to the 



* He says (p. 30) : " Der N. ophth. superf. ist wie bei Knochenfisclieu ein Ast des Trigeminus II. [=lateral line 

 component]. Der N. ojihthahnicus jirofinidus von Acipenser ist aiisschlie^slich cin Ast des Trigeminus I. tiiid ist 

 dcninach kein uoUl-ommeiics ffomoloijoii des (flcichiiamii/en Nervcii voa Lota, wcleher FAemcnte des Facialis ciUhdJi. Der 

 R. oticus ist boi Acipenser oin Ast des Facialis und des Trigeminus II. und kanu demnach aucb iiicht mit dem N. 

 ophthalmicus prof, der Knochentischc direkt vergiichen wcrden." 



SECOND SEUIES. — ZOOLOGY, VOL. VII. 28 



