206 



ICHTHYOLOGY. 



Introduc- fins, even though tlieir relative position,a.s is the case in some 

 tion- kinds of fish, sliould be in fi-ont of the pectorals, when they 



Fiff. 1. 

 Cheironeetes caudimaculattis of the family of Lophiid<t, 



obtain technically the name of jugular fins. In the above 

 woodcut we have a front view of ('heironectes caudimacu- 

 latus, belonging to a group of fish which actually tvalk at 

 times on their tour limbs. The vertical fins of fishes are of 

 a different nature, and the rays which support them, whether 

 jointed and soft, or hard and spinous, are not parts of the 

 interior skeleton, but belong properly to the skin or dermal 

 skeleton. The fins that rise vertically in the mesial plane of 

 the back, whether one or more, are named " dorsal." Those 

 from the opposite ventral aspect, situated in all cases pos- 

 terior to the vent, and therefore appertaining truly to the 

 tail, are termed " anals," and the solitary fin at the end of 

 the tail is named the "caudal." Artedi denominated the fish 

 which have spinous rays on the back, Acanthopterygians, 

 and those which have only flexible and jointed rays, Ma- 

 lacopterygians — other groups having however been previ- 

 ously detached by the forms of their branchial apparatus, 

 or the cartilaginous condition of the skeleton. Among the 

 Reptiles there are species which have dermal crests on the 

 back or tail, supported by rays, and analogous to the verti- 

 cal fins of fishes. 



In the great majority of vertebrals a lateral symmetry 

 exists externally and in the skeleton ; only one group of 

 fishes, namely, the Flounder family, presents a remarkable 

 dissimilarity in the two sides of the fish. 



All the vertebrals also agree in the separation of the 

 sexes, two individuals being required for the reproduction 

 of the species. 



SECTION II.- 



-THE EXTERNAL FORM AND CHARACTER OP 

 FISHES. 



than in other vertebrals, and only in a very few diminutive Introduc- 

 or almost obsolete. Lubricated by the surrounding medium, tio"- 

 it needs no lachrymal gland ; and as the light is tempered ^"^^/"^"^ 

 greatly by a small increase of the depth at which a fish glides 

 through the water, few species have anything like eyelids 

 or nictitating membranes. The function of nutrition is 

 very active, the appetite being very generally voracious, 

 digestion remarkably rapid, and the growth, when suitable 

 food is abundant, extremely rapid. The reproductive [)ower, 

 also, is exceedingly great. Destined to pass their whole 

 lives in a mediimi whose variations of temperature are much 

 more limited than that of the atmosphere which the other 

 vertebrals breathe, but whose conducting power is greater, 

 the temperatiu'e of fishes exceeds only by a few degrees that 

 of the water in which they swim, and their blood is cold. A 

 less vigorous respiration, therefore, suffices to keep up the 

 animal heat, and the oxygenation of the blood is accom- 

 plished by the agency of the water on certain vascular 

 organs named gills. Through these organs venous blood is 

 propelled by a simple heart, consisting of one auricle and 

 one ventricle. In these and various other parts of their 

 organization, fish preserve permanently structures that exist 

 in the higher vertebrals only in an early stage of their 

 embryonic development. Palaeontologists have ascertained, 

 moreover, that fishes were the first of the vertebrals which 

 appeared on the theatre of the earth's history, and at an 

 epoch long antecedent to the deposits in which the remains 

 of the higher animals are found. These primitive fish, 

 however, were not types of the lower forms of the class, but, 

 on the contrary, many of them were powerfully built, and 

 resembled the saurian reptiles in parts of their structure, 

 so that they were at least on par with the more highly organ- 

 ized fishes of the present day. We have not learned that 

 the remains of fish having the embryonic vermiform shape, 

 have been discovered in the oldest ichthygenous deposits. 



The Salmon is a familiar example of one of the more 

 common forms of a fish, and one frequently quoted as being 

 pre-eminently qualified for cleaving through the liquid ele- 

 ment in which it lives ; but there is a vast variety of shapes 

 to be found in the class. The common Salmonoid form 



By using the comparative terms of highest and low- 

 est class of vertebrals, we do not imply that there is 

 any deficiency in the structure of fishes which constityte 

 the fundamental group, for every creature was perfectly 

 organized when called into existence by the fiat of the 

 Creator for the functions he destined it to ])erfbrm ; but 

 He, having designed the fishes to play a part in the scale of 

 nature requiring less intelligence, has furnished them with a 

 simpler nervous system and less sentient organs, a more ob- 

 tuse sense of touch, restricted organs of smell and taste, and 

 an acoustic apparatus shut up witliin the head, without any 

 exterior ear or auditory canal for collecting and conveying 

 the vibrations by which sound is produced and transmitted. 

 Light being required to enable the fish to discover its prey 

 or avoid its enemies, the eye is larger in many of them 



Fig. 3. 



Astroncsthes niger (Chatiliodus Fieldii, Valenc.l, one of the Scopelince, a group 



of the Salmon family. 



(fig. 2) of the osseous fishes passes in different species, by 

 compression and abbreviation, to the thin vertical disks 



Fig. 3. 

 Mtlichthys vidua, one of the Balistidoe, discovered on Cook*s first voyage. 



of the ChiBtodons or Balistes (fig. 3), or, by compression 

 and elongation, into the riband-form of the Gymnetri and 



