459 



cleft ascend and grow over the mesodermal growth when they become 

 united^), the mesoderm serving as a frame- work. 



There are two reasons possible for the non-closure of the cleft, 

 either the margins of the cleft did not grow vigorously and rapidly 

 enough or the mesoblastic cells were so prolific that they kept the 

 margins asunder. 



It is highly possible and most plausible that the cleft was kept 

 open by the intrusion of the mesoblastic cells and hence the lips of 

 the cleft could not come in contact and grow together, a condition 

 absolutely necessary for the formation of the pecten and hence there 

 was no pecten. Compare Figs. 3 and 4. 



Measurements in a number of eyes of normal chick's embryos of 

 eight days show that the length of the persistent foetal cleft of the 

 ciliary region is about .25 mm. From the lower end of this cleft to 

 the beginning of the pecten measured along the coats of the eye is 

 .75 mm. 



The ciliary processes were also absent in the abnormal eyes. 



A resum6 of the subject leads to the following statements. 



1) In a normal eye of the embryo of a chick, the fissure closes 

 as early as the sixth day and in this specimen it was still widely 

 open on the eighth day. 



2) As early as the fifth day the mesoderm extends to a con- 

 siderable degree beyond the level of the inner lamella of the secondary 

 optic cup whilst in the specimen, which is the subject of the paper, 

 the mesoderm on the eighth day was only slightly above the level of 

 the lips of the cleft. 



3) In the normal, the pigment does not extend on to the inner 

 layer but in this specimen it did. 



4) As early as four days and sixteen hours, the lips of the cleft 

 are quite close together whereas in this specimen they were separated 

 by a space many times greater than normal. 



5) The ciliary processes were absent. From a study of the 

 literature, upon the subject of the closure of the foetal cleft in the 

 embryos of chicks and from a study of quite a collection of specimens 

 the following conclusions have been reached, namely that had the 

 embryo gone to maturity it would have had a large coloboma of the 

 iris, chorioid and retina. 



1) NUSSBAUM, also Bernd, 1. c. 



