ZONA PELLUCIDA IN TURTLE EGGS 243 



normal. In a few of them, however, at least one egg which must 

 already have attained a diameter of 2 to 3 mm. showed processes 

 of degeneration well under way. In several of these pathological 

 eggs I found an object which Dr. Van der Stricht and Dr. Todd 

 identified as a parasite. To the influence of this parasite the 

 pathological condition of the egg was probably due but no one to 

 my knowledge has so far made a study of this subject. 



All the eggs examined were very much less than the size of the 

 deposited egg. No essential differences are apparent in the 

 structure of the zona pellucida of the various species, hence the 

 stages described below have been chosen as representative of all 

 the material. 



The following methods of technique were employed. Fixa- 

 tion by the fluids of Hermann, Flemming or Benda, followed by 

 staining with iron haematoxylin*and Congo red or with safranin 

 and picric acid. Fixation by Bouin's mixture or trichloracetic 

 acid followed by staining either with iron haematoxylin and 

 Congo red or with Mallory's connective tissue stain. The 

 sections are cut four or five micra thick. All investigators have 

 studied their material in cross section but, judging from their 

 text and illustrations few have seen the importance of examining 

 tangential and oblique sections. Fischer mentions that he could 

 see the fiber work of the spongy layer very beautifully in tangen- 

 tial sections. In tangential sections Lams is able to interpret the 

 structure of the chorion of Osmerus eperlanus. Dr. Van der 

 Stricht called my attention to the significance of this method of 

 study. 



Because of shrinkage in paraffin and because of flattening from 

 the action of fixatives and from the pressure of the knife in cutting 

 the circumference of the egg almost always becomes ovoid: this 

 necessitates the taking of averages from measurements of the long 

 and short axes. Because also of the method of measuring with 

 the camera lucida, the figures given for the diameters of the egg, 

 taken through the zona pellucida, are only approximate. The 

 figures given for the thickness of the zona are more exact, having 

 been obtained from prints of microphotographs by computing 

 the magnification. 



