MUSEUM OF COMPARATIVE ZOOLOGY. 211 



drawn off by capillary attraction, the film soon became saturated with 

 tb^ gas, and did not need renewing. From forty-five minutes to an 

 hour, depending on the quantity of pigment, was sufficient time in 

 which to accomplish the work. Considerable difficulty was found in 

 removing the chlorine from the sections. As it had thoroughly pen- 

 etrated the tissue, simple washing, even though prolonged, did not 

 wholly remove it ; but by washing carefully, and then leaving the whole 

 slide immersed in ninety per cent alcohol for twelve or fourteen hours, 

 the gas was entirely removed. A good quality of Schallibaum's fixative 

 held the sections perfectly through all this and the subsequent staining. 



For decalcifying and hardening the tissues I have found Perenyi's 

 fluid more satisfactory than anything else tried, the two processes being 

 accomplished at the same time by this reagent. 



Of the several species of lizards which I have studied I shall describe 

 the structure in only three, namely, Phrynosoma Douglassii, P. coronata, 

 and Uta Stansburiana, these being the only ones that have presented 

 anything new or of special interest. 



Phrynosoma Douglassii. 



1. External Appearance. — Conceraing the external appearance of the 

 organ little need be said, since it differs in no essential particular from 

 what has been amply described and illustrated in numerous other liz- 

 ards. The scale marking the position of the eye is quite conspicuous, 

 especially in very young individuals, where it is of a rather lighter color 

 and larger size, relatively, than in the adult. In old individuals the 

 great development of the surrounding scales and tubercles renders it 

 somewhat less noticeable than it otherwise would be, but it is always 

 readily distinguished, not only by its median position, but also by the 

 absence of pigment and by its translucent appearance. 



2. IVie Parietal Vesicle. — Figure 1, drawn from a sagittal section 

 through the dorsal wall of the head, shows the form of the vesicle and its 

 position within the parietal foramen and with reference to the external 

 and internal surfaces of the wall. It lies within the parietal foramen, 

 though extending somewhat above the dorsal surface of the parietal 

 bone, firmly embedded in connective tissue, so that when the wall of the 

 head is separated from the brain the vesicle always goes with the former. 

 The tissues composing the dorsal wall of the head are, excepting the 

 corneous layer of the skin, quite different immediately over the vesicle 

 from those of the surrounding regions. The epidermal layer of the skin 



