664 PISCES. 



placed behind the cerebellum, which are sometimes united by a com- 

 missure : occasionally, as in the Trigla, there are as many as five pairs of 

 such supplementary masses ; but probably, instead of regarding these 

 as belonging to the brain, it would be more proper to consider them as 

 being merely the first ganglia composing the spinal cord enormously de- 

 veloped in proportion to the importance of the nerves which they give 

 off to the pectoral fins. 



(1838.) The spinal nerves of fishes arise by double roots from the 

 sides of the medulla spinalis, which generally extends from one end of 

 the canal formed by the superior vertebral arches to the other. The 

 posterior roots are dilated into ganglia soon after their origin, but the 

 ganglia are extremely minute. The spinal cord of the Moon-fish 

 (Orihagoriscus Mola) is, however, an exception to the usual conforma- 

 tion : in this remarkable fish the spinal ganglia are all collected into a 

 stunted mass placed immediately behind the brain ; and from this all 

 the spinal nerves are given off, in the same manner as those forming the 

 cauda equina in the human subject. 



(1839.) The sympathetic system in the creatures we are now exa- 

 mining is of very small size when compared with that met with in the 

 higher Vertebrata ; nevertheless it occupies the usual position, and com- 

 municates, as in Man, with the commencements of the spinal nerves. 



(1840.) There are few subjects more calculated to arrest the attention 

 of the physiologist than the progressive development of the generative 

 system in the Vertebrate classes ; and it is not a little interesting to 

 watch the gradual appearance of additional organs, both in the male and 

 female, as we advance upwards in the series of animated beings from 

 the cold-blooded and apathetic fishes. In its simplest condition, the 

 whole generative apparatus, even of a vertebrate animal, is in both sexes 

 merely a capacious gland provided with an excretory duct, wherein, in 

 the female, ova are secreted, and in the male a fecundating fluid is ela- 

 borated from the blood. The eggs of the female, when mature, are ex- 

 pelled from the nidus in which they were formed, and cast out into the 

 surrounding water. The male, urged apparently rather by the necessity 

 of getting rid of a troublesome burden than by any other feeling, ejects 

 the seminal secretion in the same manner ; and the fecundating fluid, 

 becoming diffused through the waves, vivifies the eggs with which it is 

 casually brought into contact. Such is the whole process of reproduc- 

 tion in the osseous fishes. 



(1841.) In the females of such fishes, the ovary, or roe, as it is gene- 

 rally called, consists of a wide membranous bag, ordinarily divided into 

 two lobes, but sometimes, as in the Perch, single (fig. 317, <). This 

 extensive organ, when distended with ova, fills a large proportion of the 

 abdominal cavity ; and its lining membrane is folded into broad festoons, 

 wherein the ova are formed, and lodged until sufficiently mature for ex- 

 pulsion. When ripe, the eggs escape into the cavity of the ovary, and 



