(580 



ICHTHYOLOGY. 



Structure Besides this liquid, secreted on the external surface 



and o f tjj e body, many physiologists have detected liquors 



'* in the cavity of the brain, the pericardium, and the ab- 



\ ^,-^/ domen, which we may take notice of in this place. Dr 

 Monro found the liquor surrounding the brain of a 

 skate to be of a saltish taste ; and his friend Dr Ru- 

 therford found that it contained one sixty-fifth part of 

 its weight of sea salt dissolved in it. The liquor in the 

 cavity of the abdomen contained only onfe seventy- 

 eighth part. 



SECT. XI. Organs of Reproduction. 



Organs of THE reproduction of fishes is a subject involved in 

 rcpruduc- great obscurity. The element in which they reside 

 tiou. conceals from us the actions which they perform, and 



hence we are unable to point out with certainty the 

 uses of the different organs, or the functions which they 

 exercise. Even in the days of Aristotle the difference 

 in the mode of reproduction between the cartilaginous 

 and the osseous fishes had been observed ; and although 

 many accurate observations have been made by modern 

 zootomists, much still remains to be done both in the 

 field of observation and dissection. 



In the general view which we propose to give of this 

 subject, fishes may be divided into two classes, distin- 

 guished by their reproductive organs. Thus, some 

 have the sexes distinct, while in others they are united. 

 Those with the sexes distinct may be subdivided into 

 the oviparous and the false viviparous, or ovovivipa- 

 rous. 



Sexes dis- 1 Oviparous Jlshes, with the sexes distinct. The fishes 

 tinct. Ovi- included under this division are by far the most nume- 

 parous. rous. They have all free branchiae Some of them 

 possess a cartilaginous skeleton, while others belong to 

 the division termed osseous. In all, the egg is impreg- 

 nated externally, and arrives at maturity without the 

 aid of the mother. 



In the males of this division, the testes, known by 

 the name of milts, are two in number, of a white colour, 

 and lengthened form. The surface is usually irregular- 

 ly tuberculated. They are situated on each side of the 

 abdomen, and consist of glandulous sacs destined for 

 the preparation of the impregnating fluid. Through 

 the middle of each milt there passes a ductus deferens, 

 uniting with each other at the posterior part of the ab- 

 domen, and forming a kind of vesieula seminalis. The 

 external opening for the issue of the semen is in some 

 in the cloaca, while in others there is a small orifice si- 

 tuated behind the anus, which gives vent to the sexual 

 evacuations. 



In some of the oviparous abdominal fishes, there are 

 two cartilaginous fins situated between the ventral fins, 

 and supposed by La Cepede to be the external openings 

 of the sexual organs. They are termed by him Appen- 

 dices genitals 



We possess few accurate experiments on the chemi- 

 cal composition of the seminal fluid of fishes. Fourcroy 

 published in the Annales de Chim. vol. Ixiv. p. 3. some 

 experiments on the milt of the carp. It was neither 

 acid nor alkaline. It appears to consist of albumen, 

 gelatine, phosphorus, phosphat of lime, phosphat of 

 magnesia, and muriat of ammonia. More recently, Dr 

 John subjected the milt of a tench to a chemical analy- 

 sis, and obtained the following ingredients : water, in- 

 soluble albumen, gelatine, phosphat of ammonia, phos- 

 phat of lime, phoipliat of magnesia, and alkaline phos- 

 phat. He could not detect the presence of any phos- 

 phorus, which had been given as a constituent by 

 1 



Fourcroy and Vatiquelin. In H these examples, how- 

 ever, the seminal fluid was mixed with the substance of 

 the testes. 



In the females of this division, the ovary, usually 

 termed the roe, is double in the greater number of fishes, 

 but in a few it appears to be single. It occupies near- 

 ly the same position as the milt in the males. It con- 

 sists of a thin delicate membrane inclosing the ova. 

 These are generally disposed in transverse layers, con- 

 nected by means of blood vessels. There is no distinct 

 oviduct. The external openings are similar to those in 

 the male. 



Previous to the deposition or ejection of the roe or 

 eggs by the female, a union has been formed with a 

 male. But this connection is merely temporary, and is 

 dissolved immediately after the impregnation of the 

 egg has taken place. In the Cyclopterus lumpus, how- 

 ever, it is stated that this connection is of longer dura- 

 tion, that they continue to watch over the eggs with ten- 

 der solicitude, and defend them from the rapacity of 

 other fishes. The pleasure derived from the belief in 

 this singular example of parental care, is in a great 

 measure destroyed by the hint which has been thrown 

 out, that they defend the eggs from the attack of other 

 fishes, that they may appropriate them as a feast to 

 themselves. 



The ova are first deposited by the female, and thes 

 the male pours upon them the impregnating semen. In 

 many instances, they form a hole in the sand, by their 

 mutual assistance, and place therein the roe ; in other 

 instances, the roe is deposited in the crevices of rocks, or 

 on sea weeds or aquatic plants. But it would be endless 

 to detail the various ways (even were we better ac- 

 quainted with them than we profess to be) in which 

 fishes perform this curious function of their nature. 



The eggs of fishes are very various with respect to 

 colour, but agree in being of a spherical form. The 

 integument is more or less firm according to the species. 

 The yolk, instead of occupying the centre, as in the 

 eggs of birds, is placed laterally, and is surrounded by 

 the glaire or albuminous matter. Between the yolk 

 and the glaire, is situated the germ or embyro. The 

 germ becomes ready for exclusion at very different pe- 

 riods, according to the species. Thus the egg of the 

 carp is said to be perfected in the course of three weeks, 

 while that of the salmon requires as many months. But 

 in the eggs of the same species, a great deal depends 

 on the temperature to which they are exposed. In the 

 same pond, those eggs are soonest hatched which have 

 been deposited in the shallowest water. 



As the embryo is developed, the heart first appears, 

 afterwards the spine, eyes, and tail. The organs of 

 motion are evolved in the following order. The pectoral 

 fins first make their appearance, and afterwards those 

 of the tail ; the dorsal fins follow, and then the ventral 

 and anal fins. 



2. Ovoviviparous Jishes, with the sexes distinct. In Sexes dis- 

 this division are included the chondropterygii, and like- t '. nct> O vc 

 wise a few osseous fishes Sexual intercourse takes V1V1 P !U< 

 place, and the eggs are hatched in the uterus, and ex- 

 cluded along with the fry. 



In the males of this division, at least in those of the 

 ehortdropterygii, the testes are two in number, flat, of 

 great extent, and situated between the spine and the 

 stomach and intestines. Each is divided into two por- 

 tions ; the first resembles the soft milt of oviparous 

 fishes, and the second consists of small spherical glan- 

 dular bodies. From these an epididymis is produced, 

 chiefly composed of convoluted tubes, which terminate 



