OP VERTEBRATE ANIMALS. 65 



ovaries are not less voluminous; most of them first lay their 

 eggs, and afterwards the male fecundates them; with some, 

 however, copulation and an intromission of sperm takes place, 

 the latter heing mostly ovoviviparous. The muscles which form 

 so large a portion of the mass of their bodies are white, exces- 

 sively irritable, and are less perfectly organized than those of 

 the other classes. It is the same with the bones: in some of them 

 (thechondropterygii) the bones remain cartilaginous: the cal- 

 carious substance forms no filaments, but remains in isolated 

 grains: in some of them, even the articulations of the spine do 

 not exist, and iu the others, the bones, although fibrous and 

 calcarious, differ greatly in solidity, and are remarkably at 

 variance with those of the other classes. The ribs are often 

 soldered to the transverse apophyses. The senses are imper- 

 fect; the nostrils are mere rudimental pits at the end of the 

 nose; the cornea of the eye is flat, there is but little aqueous 

 humour, and the crystalline is almost spherical; the ear con- 

 sists of a vestibulary sac in which are suspended bones of a 

 stony hardness, and in three semi-circular membranous canals, 

 commonly placed in the hollow of the cranium: some genera 

 only have a fenestra ovalis, opening externally; the tongue is 

 most commonly bony and dentated, or horny; the whole skin 

 of the greater portion of them is covered with scales. Some 

 have fleshy cirri or filaments, which may serve for the sense of 

 touch. The prolongation of the spinal marrow into the cra- 

 nium terminates anteriorly by enlargements, whence originate 

 the olfactory nerves. 



The class of fishes in the nature of the skeleton, and in the 

 mode of generation, offers a tolerably well defined division, 

 viz. the cartilaginous, and the bony. 



It is in this class of the vertebrata that we find a genus (that 

 of the pleuronectes or flat fishes) where the head is defective in 

 symmetry, such as the two eyes being on the same side. 



59. Reptiles offer in their figure, in their structure, and in 

 their functions, much greater varieties, than any of the three 

 other classes of the vertebrata. In fact, some have four feet, 

 others have two before, a third, two behind, and a fourth, 

 none at all. In some, the body is covered with scales, in others, 



