304 



JAMES ROLLIN SLONAKER 



for a short distance, then much more rapidl3^ This thinner 

 region may be termed the first indication of the pars caeca. 

 There is, however, no decided mark to indicate its extent. At 

 this time changes are taking place in the adjacent pigment and 

 chorioid layers, which is the early formation of the ciliary bodies. 

 The nine-day embryo shows a decided reduction in thickness 

 of the retina a short distance from the pupillary border (figs. 



TABLE 5 

 Measurements in the region of the ora serrata of the different layers of the retina, 

 the whole retina, the chorioid and sclerotic layers at different ages. Measurements 

 are in millimeters, 2 to 13 represent the age in days of the embryos used; H-2, 

 hatched two days; H-4, hatched four days; H-fl, young just flying 



days 



2 



3 



4 



5 



7i 



8 



10 



12 



13 



H-2 



H-4 



H-fl 



Adult 



008 

 0.012 

 0.010 

 0.006 

 0.004 





0.024 

 0.016 



5e 



0.024 0.020 

 0.026 0.020:0 

 0.014 0.032 

 0. 026 jO. 040 

 036;0 024j0 



044 

 048 

 056 

 056 

 060 

 044 

 096 

 140 

 088 

 074 10 



052:0 



032 

 024 





0.008 0.012 



008 

 012 

 004 

 004 



< a 

 o o 



o " 



0.004 

 0.008 



Z 3 

 S B 



0.024 

 0.024 

 0.030 

 0.028 

 0.024 

 0.028 

 004 

 0.008 

 0.008 

 0.006 



0.010 

 0.012 

 0.009 

 0.012:0.012 012 



0.006 

 0.007 



0.007 

 0.006 



068 

 072 

 086 

 084 

 084 

 072 

 024 

 164 

 172 

 164 

 145 

 130 

 128 lO 



016 

 008 

 004 

 024 

 032 

 024 

 016 



016 

 016 

 016 

 032 

 012 

 024 

 020 



0.044 

 0.028 

 0.020 

 0.020 

 0.024 

 0.008 

 0.012 



38 and 69). This rather abrupt thinning of the retina occurs 

 0.4896 mm. from its anterior margin. It is the first indication 

 of the true ora serrata so far observed. The thin portion, the 

 beginning of the pars caeca, extends to the lens, with which it 

 is in close contact. This modification in thickness is more 

 noticeable on the temporal than on the nasal side of the lens. 

 Associated with this change in the retina is the noticeable advance 

 in the development of the ciliary body and the iris. A portion 

 of the retina and pigment layer extends over the front of the 



