322 FISHES. 



and a pipe-fish (Solenostoma), where they are carried in a pouch formed by the 



coalescence of the broad pelvic fins with the skin of the body, is the female known 



to take any care of her eggs after spawning. Among the bony fishes there are, 



however, several instances where the young are more or less carefully tended by 



the male parent; some, like the sticklebacks, building a nest, while others, like 



certain pipe-fishes, have an abdominal pouch in which the eggs are hatched. 



The eggs of sharks, rays, and chimaeroids differ remarkably from those of bony 



fishes, being large in size, few in number, and laid singly instead of in masses. 



They are invested in a hard horny envelope, which is generally oblong in form, 



with the four corners produced, and frequently elongated into tendrils by means of 



which the egg is moored to some foreign substance. The males of these fishes are 



armed with organs known as claspers, which are partially ossified processes arising 



from the pubis, and are evidently connected with the function of reproduction. 



The young of many fishes differ markedly from the adult ; and certain peculiar 



creatures with long ribbon -like bodies and small heads, for which the name of 



Leptocephali has been proposed, are believed to be the young of littoral fishes which 



have been carried out to sea, where they have undergone an altogether abnormal 



development. The changes which take place in the flat-fishes during development 



may be more conveniently noticed under the heading of that group. Although 



male and female rays differ remarkably from one another in the structure of their 



teeth, while both in this group and in the sharks and chimaeroids the males are 



distinguished by the possession of the aforesaid claspers, there is generally but 



little sexual difference among fishes. In the bony fishes, however, the females are 



larger than the males; among the cyprinodonts the difference between the two 



being occasionally as much as six times. 



Fishes exhibit a remarkable degree of difference in regard to 

 Tenacity of Life. . „ , . . ° 



their power of bearing changes from their normal environment. On 



this subject Dr. Giinther writes that, " some will bear suspension of respiration — 

 caused by removal from water, or by exposure to cold or heat — for a long time, 

 whilst others succumb at once. Nearly all marine fishes are very sensitive to 

 changes in the temperature of the water, and will not bear transportation from one 

 climate to another. This seems to be much less the case with some fresh-water 

 fishes of the temperate zone ; since carp may survive after being frozen in a solid 

 block of ice, and will thrive in the southern parts of the temperate zone. On the 

 other hand, some fresh- water fishes are so sensitive to a change in the water that 

 they perish when transferred from their native river into another apparently 

 offering the same physical conditions. Some marine fishes may be abruptly trans- 

 ferred from salt into fresh- water, like sticklebacks; others survive the change 

 when gradually effected, as many migratory fishes ; whilst others, again, cannot 

 bear the least alteration in the composition of the salt-water (all pelagic fishes). 

 On the whole, instances of marine fishes voluntarily entering brackish or fresh- 

 water are very numerous, whilst fresh- water fishes proper but rarely descend into 

 salt water." 



The foregoing remarks lead naturally to the subject of the dis- 

 Distribution. . fe & _ .j j 



tribution of fishes ; a subject which the limits of space compel us to 



dismiss with a few sentences. In the first place, we find that many marine fishes 



