ICHTHYOLOGY. 



Structure 

 and 



" I found, (says he, Phil. Trans. A.D. 1815, Part II. 

 p. 266), upon examination, that the two glandular bo- 

 dies projecting into the belly, one on each side of the 

 y_j-j ovariutn, which have always been supposed to be the 

 kidneys, varied very much in size and appearance at the 

 beginning and end of the season. When the ova are 

 so small that the animal is reputed to be a male, these 

 glandular bodies, and the black substance upon which 

 they lie, appeal' to form one mass, and the duct upon 

 the anterior part is thin and almost transparent, con- 

 taining a fluid equally so; but in the end of May, when 

 the ova increase in size, these glandular bodies become 

 larger, more turgid, and have a distinct line of separa- 

 tion between them and the black substance behind ; 

 their structure is more developed, being evidently 

 composed of tubuli running in a transverse direction, 

 and the ducts leading from them are thicker in their 

 coats, and larger in size. 



" On the 5th of June, the ova were found to be of 

 the full size ; and a small transparent speck, not before 

 to be observed, was seen in each ; at this time the tu- 

 bular structure had an increased breadth, and the duct 

 going from it contained a ropy fluid, which, when exa- 

 mined in the field of the microscope, was found to be 

 composed of small globules in a transparent fluid. On 

 the 9th of June, neither the ova nor the tubular struc- 

 ture had undergone any change. On the 1 1th of June, 

 the ova were of the same size, but the slightest force 

 detached them from the ovarium ; the tubular struc- 

 ture had increased still more in size, the fluid in the 

 ducts was thicker, more ropy, and when water was ad- 

 ded to it in the field of the microscope, it coagulated, 

 and what was before made up of globules, had now the 

 appearance of flakes. The ova do not pass out at an 

 excretory duct as in fishes, but drop from the cells in 

 the ovarium in which they were formed, into the cavi- 

 ty of the abdomen, and escape by two small apertures 

 at the lower part of that cavity, into a tube common to 

 them and to the semen in which they are impregnated." 

 In the lampern or pride, and in the gastrobranchus cce- 

 cus, a similar structure is observable." 



Although these observations leave little room to doubt 

 that the animals in question are hermaphrodites, still it 

 remains to be determined at what precise period, or in 

 what position, the eggs are impregnated. 



Although the sexual organs of fishes had been long 

 known, it was not until the middle of the 1 8th cen- 

 tury that any experiments were performed to ascertain 

 the effect of their abstraction. Tully appears to have 

 been the first person who performed the operation, and 

 an account of his experiments has been published in 

 the Gent. Mag. vol. xxv. p. 416, and in Phil. Trans. 

 vol. xlviii. When the abdomen of the fish is laid open, 

 and the milt or roe carefully separated, and the wound 

 sewed up again, the fish appears to experience but lit- 

 tle pain, and the wound heals in a few weeks. These 

 experiments have frequently been performed on the 

 carp, and they are attended with little risk. The fish 

 grows to a larger size, and its flesh is said to have a more 

 delicate flavour. But castration has never come into 

 general use among the proprietors of fish ponds, being 

 seldom performed but from motives of curiosity or 

 seience. 



We have already stated, that the impregnation of the 

 egg takes place without the body of the female, and 

 the experiments which have been conducted to esta- 

 blish this point, have likewise made us acquainted with 

 the existence of hybrid Jishes. Even in a common fish 

 pond, where carp and trout are permitted to live in 



Castration. 



of Fishes. 



Number of 



company, the carp sometimes impregnates the eggs of Structure 

 the trout, or the trout those of the carp. The limits, Bntl . 

 however, within which this irregularity is confined, 

 have never been investigated with care. 



Fishes exhibit very remarkable differences in regard 

 to the number of eggs which they produce. The rays 

 and sharks seem to prepare but a very limited number. ej 

 Rondeletius states the number in the Squalus acanthias 

 at six ; other observers have found in other species 26 

 and even 30. But the number of eggs in other kinds 

 of oviparous fish, exceeds almost our powers of rec- 

 koning. The following Table (Phil. Trans. 1767), 

 may convey to the general reader some idea of their 

 prolific powers. 



Hybrid 

 fishes. 



It appears evident, from this Table, that there is no 

 regular proportion between the weight of the fish and 

 the weight or number of eggs produced. Nor is there 

 any estimated proportion between the number of eggs 

 deposited, and the number of fish which arrive at ma- 

 turity. The eggs are eagerly sought after by other 

 fishes, by aquatic birds and reptiles. In the young 

 state, they are pursued even by their own species, as 

 well as by beings belonging to other classes. But for 

 the numbers of eggs thus produced, the very race of 

 fishes would soon be extinguished by enemies while 

 young ; and we may add, that the diminution of the 

 number of eggs would cut off a large supply of food, 

 and destroy that dependence which we observe in the 

 polity of nature, of the different races of animals on 

 one another. 



The season in which fish deposit their eggs varies 

 according to the species, and even the habit of the in- 

 dividual. It is well known that among salmon, even 

 in the same river, a difference of some months is ob- 

 servable, and we believe that the same remark is ap. 

 plicable to all other kinds of fish. In general, before 

 spawning, fish forsake the deep water, and approach 

 the shore, that the roe being placed in shallow wa- 

 ter, the influence of the solar rays may vivify it. At 

 that season, some fish forsake the salt water, and as- 

 cend rivers, and after spawning, retreat again to the 

 ocean. 



The eggs of various species of fish belonging to the 

 oviparous order, with distinct sexes, are used as articles 

 of food. Where circumstances permit, they are con- 

 sumed while in a recent state. In other situations they 

 are salted, and form the well-known article of trade 

 caviar. 



The characters which the organs of reproduction fur- 

 nish, in the discrimination of species, have been hitherto 

 1 



