21 



also to the vitreous body and to part of the retina, which for a long- 

 time has no blood vessels of its own. This functional interde- 

 pendence of blood vessels, vitreous fibers, and retina might offer a 

 teleological explanation for the intimate protoplasmic union of these 

 parts described in chapter II. As soon as the hyaloid system has 

 discharged this nutritive function, a process of resorption sets in. 

 This process does not always begin from the extremities of the 

 branches; it first manifests itself by a general decrease in the dia- 

 meter of the blood vessels, which may thus be cut up into a number 

 of parts found scattered in various places of the vitreous body. 

 These parts gradually disintegrate and give rise to many cellular 

 elements which are met with in more advanced stages of develop- 

 ment and sometimes even in the eyes of adult animals. They are 

 the remnants of the hyaloid vascular system. The gradual resorp- 

 tion of the blood vessels does not proceed in a uniform manner in 

 all embryos, as a comparison of embryos of 130, 150, and 180 mm 

 length shows, but in the eyes of embryos of 200 mm, only the main 

 trunk, the hyaloid artery proper, remains (Figure 17). It may be 

 added here that the main trunk was found also in a practically 

 mature fetus 12 inches in length, which makes it probable that com- 

 plete resorption of the hyaloid artery takes place at the time of 

 birth or even later. In the eye of a full grown animal, a piece of 

 the hyaloid artery, about 6 mm long, was still present attached to 

 the lens. Together with the hyaloid system the remaining meso- 

 dermal elements also undergo a process of disintegration. 



What then is the fate of the fibrous network which we found in 

 such intimate union with the mesoderm in the previous stages of 

 development f It is probable that a portion of it also disintegrates 

 and is resorbed. But it is no less probable that the remaining por- 

 tions make up the loose fibrous tissue found in the hyaloid canal and 

 in the more fluid parts of the vitreous body. The reasons for this 

 assumption will be given below. 



We must first turn our attention to another structure, a clear 

 conception of the formation and the significance of which will throw 

 more light on the present investigation. This structure is the hya- 

 loid canal. We have already called attention to the wide difference 

 in the diameter of the hyaloid artery and the so-called hyaloid canal, 

 and expressed our doubts that the latter represents nothing but the 

 cavity left for a time after the former has been resorbed. This 



