736 LECTURE LIX. 



in both: their eggs are involved in a membrane, and have no albumen* 

 Of the six orders of fishes, four have regular gills, supported by little bones; 

 and they are distinguished, according to the place of their ventral fins, into 

 apodes, as the eel and lamprey; jugularis, as the cod; thoracici, as the 

 sole and perch, and abdominales, as the salmon and pjke : distinctions 

 which appear to be perfectly artificial, although useful in a systematic 

 ' arrangement. Tiie two remaining orders are without bones in the gills, 

 those of the one being soft, and of the other cartilaginous or gristly. 

 These are the branchiostegi and chondropterygii of Artedi, which Linne, 

 from a mistake, classed among the amphibia. The sun fish, the lump fish, 

 the fishing frog, and the sea horse, are ofvthe former, and the sturgeon, the 

 skate, and the shark, of the latter order. 



Insects derive their name from being almost always divided, into a head, 

 thorax, and abdomen, with very slender intervening portions: although 

 these divisions do not exist in all insects. They are usually oviparous : they 

 respire, but not by the mouth; they have a number of little orifices on each 

 side of the abdomen, by which the air is received into their ramified tracheae; 

 and if these are stopped with oil, they are suflfocated. Instead of bones, they 

 have a hard integument or shell. Their mouths are formed on constructions 

 extremel)- various, but generally very complicated : Fabriciushas made these 

 parts the basis of his classification; but from their minuteness in most species, 

 the method is, in practice, insuperably inconvenient; and the only way, 

 in Avhich such characters can be rendered really useful, is when they are 

 employed in the subdivision of the genera, as determined from more con- 

 spicuous distinctions. Insects have most frequently jaws, and often 

 several pairs, but they are always so placed as to open laterally or horizon- 

 tally. Sometimes, instead of jaws, they have a trunk, or proboscis. In 

 general, they pass through four stages of existence, the egg, the larva, or 

 stage of growth, the pupa, or chrysalis, which is usually in a state of torpor 

 or complete inactivity, and the imago, or perfect insect, in its nuptial, 

 capacity. After the last change, the insect most frequently takes no food 

 till its death. 



The Linnean orders of insects are the coleoptera, with hard sheaths to tlieir 



2 . ' 



