THE PINEAL SYSTEM OF AGAMID& 273 



kind of parachute or gliding apparatus by which the animal is enabled 

 to pass by long leaps from tree to tree. There is also the frilled lizard, 

 Chlamydosaurus, which has a whig-like expansion growing out around 

 the head, neck, and shoulders. It is found in sandy deserts, has a long 

 tail, and walks with long strides on its hind legs. The family includes 

 the horned-lizard, Ceratophorus aspera ; Calotes versicolor, which, like 

 the chameleon, is capable of changing its colour ; the thorny-tailed 

 lizard, Uromastix ; and the Australian lizard, Moloch horridus, which is 

 covered all over with large conical spines. 



In this family a parietal foramen, parietal scale, and parietal spot 

 are described as being present in most of the species that have been 

 examined, though these differ in their degree of development. Thus, in 

 Ceratophorus the foramen is only indicated by vessels traversing the 

 bone, while in Calotes ophiomachus all three are specially well developed. 



In Agamidae a parietal organ and end vesicle are not as a rule both 

 present in the same individual ; hence it is often difficult to determine 

 whether the organ found lying in the parietal foramen is the parietal 

 sense organ or the end vesicle of the pineal organ, more especially as 

 the " eye " is in most cases not separated from the stalk of the epiphysis ; 

 moreover, in some cases there is no distinct differentiation into lens and 

 retina, and no pigment. A differentiated eye is, however, definitely 

 present in Calotes, Agama, Phrynocephalus, and Grammatophora. More- 

 over, in an adult specimen of the latter described by McKay (1888) the 

 parietal eye was separated from the epiphysis, as in Lacerta vivipara or 

 Sphenodon. It showed a biconvex lens and a well-differentiated retina, 

 in which McKay distinguished rod-like cells, round cells, a molecular 

 layer, a layer of spindle-formed elements, and special triangular cells 

 (? multipolar nerve cells) ; pigment was deposited in horizontal layers 

 in the rod-like cells, and a corneal scale was present. Speaking generally, 

 in those cases in which a well-developed parietal foramen, parietal scale, 

 and parietal spot are present, the parietal eye is well developed. In cases 

 such as Ceratophora, in which the existence of a parietal foramen is only 

 indicated, it is doubtful whether the imperfectly developed organ beneath 

 it really represents a parietal sense organ or is a modified end vesicle, the 

 parietal organ being absent. 



Draco volans. 



Spencer described a parietal organ having the form of an ovoid vesicle, 

 the longest diameter of which lay in the median plane. There was no 

 differentiation into lens and retina. Pigment was absent in the vesicle 

 itself, but was present in the connective tissue membranes behind the 

 vesicle. It lay in a parietal foramen, the position of which was in most 

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