REPTILES 195 



The sternum is an insignificant lozenge-shaped piece of car- 

 tilage, running back behind into a couple of slender rods, with 

 which the hinder sternal ribs are united, while the others connect 

 with the two posterior sides of the lozenge. 



Skeleton of Limbs. This is in many ways interesting, being to 

 a large extent of what is called " generalized type", an expression 

 which deserves a little examination, as it embodies an important 

 idea constantly recurring in biological works. It often happens 

 that in examining a series of human contrivances designed to meet 

 the same or a similar end, a kind of general plan or similarity will 

 be found to run through all of them. Under such circumstances 

 it would very likely be possible to pick out some one of the series 

 which might be looked upon as embodying the ideas involved in a 

 general kind of way, and from which, by modification, the other 

 members of the series might be derived. This case would form a 



o 



generalized type of the entire series. A good instance is that of 

 various kinds of habitation, of which the moderate-sized houses 

 which make up a formal row may be taken as generalized types. 

 In such a house would probably be found, among other apart- 

 ments, breakfast-room, dining-room, drawing-room, study, and a 

 certain number of bedrooms, all these, let us suppose, of reasonable 

 size, and square or rectangular shape. Modifications of such an 

 average plan might be effected in one or more of the following 

 ways: (i) Variation in shape', the dining-room, for example, 

 might be oval or polygonal. (2) Variation in relative size: the 

 drawing-room, say, might be the same size as the dining-room, or 

 smaller, or it might be larger. (3) Variation in number, either on 

 the side of increase, as by addition of a second drawing-room, or 

 on the side of decrease, as by reducing the number of bedrooms. 

 In the latter case a particular sort of room, perhaps the study, 

 might be made so small as to deserve the name of a ''vestige", 

 and the next step would be its complete suppression. (4) Coales- 

 cence, or fusion of rooms, as, for instance, by complete or partial 

 removal of the party- wall separating two adjoining rooms. By 

 application of these principles of alteration, a small cottage on the 

 one hand, or a castle on the other, might be referred to the same 

 type as the average house, and it is obvious that dwellings of all 

 styles and sizes are, after all, neither more nor less than houses 

 or places of human habitation, and must fulfil certain average 

 requirements. It may also be noted, in passing, that the house 



