457 



turn inwards towards the lens, are very close together with a blood- 

 vessel and some mesodermal cells lying between them (Fig. 1). 



As the cleft passes backwards, within the width of a few sections, 

 it widens rather abruptly and continues with a wide interval. 



Normally in the ciliary region the lips of the cleft turn outwards 

 (Fig. 1 ^), with the inner retinal layer facing whereas the lips of the 

 posterior part are turned inwards towards the vitreous with the pig- 

 ment layer facing ^). By comparing Fig. 1 and 2 it can easüy be seen 

 that the lips of the abnormal specimen are inverted instead of everted. 

 It is just in this region, where the cleft remains open during life, that 

 the retinal cells of the inner layer become pigmented but in the ab- 

 normal specimen the pigment can be seen passing from the outer 



(normal) 



(almormal) 



Fig. 1. 



Fig. 2. 



r equals the inner layer of the optic cup. p pigment layer, m is mesoderm. 

 Sk is prochondra of the sclera, cl is the foetal cleft. Pis pecten. Abnormal and normal 

 of eight days compared. 



Figs. 1 and 2 represent abnormal and normal sections from the ciliary region, 

 but the abnormal is a little farther back than the normal ; they show the inversion and 

 eversion of the margins of the cleft. The ciliary processes are present in the normal 

 and absent in the abnormal. 



layer over into the inner retinal layer (Fig. 8), which is contrary to 

 the normal state. 



As the cleft passes backwards its lips are directed towards the 

 vitreous in such a manner that the outer pigment layer touches the 

 mesodermal cells which fill the gap. These mesodermal cells are 

 continuous with the cells which form the foundation of the chorioid. 

 They form a rather loose net-work in which lie many small blood- 



1) M. NUSSBAUM, Archiv f. mikrosk. Anat., Bd. 57, 1900, p. 347, 

 and Bd. 58, 1901, p. 201. — Bernd, Die Entwickelung des Pecten im 

 Auge des Hühnchens aus den Blättern der Augenblase, Bonn 1905, 

 p. 25. 



