276 ADAPTATIONS TO SPACE AND MOTION 



This is further aided by two other devices, the ciUary processes and 

 the 'Ringwulst', or 'annular pad' (Fig. 109). CiUary processes are to 

 be sharply distinguished from ciliary folds. The latter may be radial 

 or circular and are always low affairs whose significance is solely the 

 increase of the secretory or absorptive surface of the thin layer of blind 

 retinal tissue which covers them, the ciliary epithelium. The folds on the 

 posterior surface of the amphibian iris (there being no room for them 

 on the narrow ciliary body) are in the same category. 



Ciliary processes differ morphologically from ciliary folds only in a 

 quantitative way, but they have a separate physiological significance. 

 They are tall, fin-like structures (Fig. 110) and serve to bring the 

 ciliary body into firm contact with the lens, with which (in Saurop- 

 sida) their tips are actually fused. The ciliary body, if it lacked them, 

 might still be made to reach to the lens equator and contact the annular 

 pad smoothly all the way around. But, there would be two difficulties 

 about such an arrangement. The more grave one would be that the 

 retrolental space would be sealed off from the posterior chamber so that 

 aqueous could not transfer back and forth between the two during 

 accommodation, as it is free to do between ciliary processes. Also, the 

 ciliary body would tend to be 'muscle-bound', with a great deal more 

 internal friction during the action of its muscles, if its constrictive force 

 were not transferred indirectly to the lens through the ciliary processes. 

 If one imagines the spaces between the processes to be filled in with 

 solid material, one can see that as the ciliary zone decreased in diameter, 

 this material would have to be compressed; and the energy required for 

 this useless compression would be lost from the effective action of the 

 ciliary muscle upon the lens. Only the lizards have been able somehow 

 to reduce the size of the processes almost to the vanishing point and still 

 employ the standard sauropsidan method of accommodation. They may 

 have some difference in the mechanics or hydraulics of the phenomenon 

 which accounts for their heresy. 



While the scleral ossicles and the ciliary processes extend the ciliary 

 body axiad to meet the lens, the latter comes half-way, so to say, by its 

 production of the annular pad. In Sauropsida, after the ordinary circum- 

 ferential lens fibers have been laid down, the lens epithelium in the 

 equatorial region does not remain simply cuboidal or columnar. Its 

 cells elongate enormously, without swinging their axes through 90 to 

 become ordinary circumferential lens fibers (compare Fig. 109, ap, with 

 Fig. 41a, p. 111). The result is an equatorial thickening on the lens, 



