212 Journal of Compauative Neuk()lo(;v. 



Siluridae should be placed among the most highly specialized 

 bony fishes, though this, of course, does not necessarily 

 involve a position high in the scale, phylogenetically con- 

 sidered. 



The present contribution is based upon the study of 

 dissections and histological preparations of such species of 

 Siluridse as are most accessible in the Ohio Valley., viz., 

 Amiurus catus gill, Pilodictis olivaris Gill and Jordan, 

 Ictalui'us punciatus Jovda.n, and Ictalurus lacustris Gill and 

 Jordon. The adult brains of these species are so nearly alike 

 that it would be difficult to distinguish them externally, and 

 in the following descriptions the statements apply to all of 

 them unless otherwise expressly indicated. In the case of 

 some of our large river cats especially, and probably of the 

 other species also, the brain practically ceases to grow when 

 the fish attains a moderate size, even though the weight of 

 the body may afterward increase many fold. A specimen of 

 the mud cat, Pilodictis olivaris, for instance, weighing 

 twenty-one pounds, had a brain which, when hardened, 

 could scarcely be distinguished by careful measurements 

 from that of another specimen weighing less than five pounds. 

 The cranial cavity, however, enlarges more nearly in pro- 

 portion to the size of the head. In large specimens it is more 

 than twice the size of the brain, which lies in the ventral and 

 caudal portion. In the remaining space an oily arachnoid 

 tissue is closely packed around the emerging nerves. In 

 smaller specimens the brain is much larger in proportion to 

 the head until in individuals one inch long it fills the entire 

 cranial cavity and, in fact, almost the entire head. 



Measurements. — The following measurement are taken 

 from an alcoholic brain of Pilodictis olivaris. Other measure- 

 ments in the text refer to the same specimen. This fish was 40 

 cm. long, and would weigh about four pounds. The measure- 

 ments, however, would be almost equally exact for the brain 

 of a specimen weighing twenty pounds: Length of brain from 

 end of cerebrum to exit of dorsal root of vagus, 17 mm.; 



