308 The Field Naturalist's Quarterly November 



the specialised, by means of natural selection acting upon 

 ever-occurring morphological variations. 



It naturally follows that locomotion in lizards will be of 

 different kinds, according to the state of development or 

 absence of limbs. The two extremes are, of course, the 

 quick, running movements of the lizards with perfect fore- 

 and hind-limbs, and the quiet, gliding motion of the entirely 

 limbless forms, like the slow-worm. In intermediate forms 

 the method of progression is likewise modified, sometimes 

 exhibiting bipedal locomotion, the hind-limbs only being 

 used. If the four limbs are very small in proportion to the 

 body, the locomotion is correspondingly sluggish. Along 

 with the variations in the limbs themselves there have 

 occurred alterations in the muscular structures to enable 

 the reptile to adopt the new mode of locomotion, and other 

 organs have become similarly modified for their particular 

 functions in the changed conditions of life. 



It is only necessary to study the respective movements 

 of different kinds of lizards to appreciate what a wonderful 

 amount of specialisation has taken place in connection with 

 this function alone, and the reader who would pursue this 

 interesting topic is recommended to turn his attention to the 

 geckos, skinks, and the slow-worm, to observe the immense 

 variety of movements which have resulted from structural 

 modifications. He will then naturally turn his attention 

 to the question of the relationship of the lizards to the 

 snakes, observing that in some families, that of the boa- 

 constrictor for example, snakes have external indications 

 of limbs in the shape of spurs, a subject which is 

 beyond our province here. 



The general conclusions to be drawn from an exam- 

 ination of all the lizards which exhibit some stage of 

 degeneration in the limbs, are summed up by Professor 

 Cope somewhat as follows: — It is obvious that degeneracy 

 of the scapular and pelvic arches to which the fore- and 

 hind-limbs are attached when present, sooner or later 

 follows partial or complete loss of the limbs themselves. 

 In the Diploglossa (lizards with papillose tongues), the 

 fore-limbs have disappeared more generally than the hind- 

 limbs. In the skinks the limbs incline to degenerate more 



