26 The American Naturalist. [January. 



too sharp. At the same time reach forward with the point of 

 the needle and pierce the suspensory ligament and iris in order 

 to open the aqueous chamber. In doing this, care is taken 

 not to injure structures in the plane of the desired sections. A 

 cannula of suitable size, being connected with a siphon from 

 A or A', is filled with the liquid and inserted. The cannula 

 should have a fine smooth point. Great care is taken in in- 

 serting it so that the stream of fluid is not directed behind the 

 retina to float it off. A hole is now made in the opposite side 

 of the eye, the aqueous chamber again pierced and all aqueous 

 } animals this 



hui, 



d vitreous humor allowed to 

 very much more gel- 



atinous than in others, and re- 

 quires much more pressure to 

 remove it. The hole below is 

 then stopped with a small glass 

 plug (Fig. 2, B), and the eye 

 immersed in hardening fluid 

 (Fig.l,B). The bottles are now 

 covered as tightly as possible 

 with tinfoil to prevent evapora- 

 tion and entrance of dust parti- 

 cles. The cannula and stopper 

 should fit so tight that there is 



) leak. In 



'very < 



■ the i 



entation of the eye is marked 



before it is removed from the 



head. This is done by sewing a small tag to the outer layers 



of the sclerotic (Fig. 2, C). 



The pressure varies greatly with the kind of eye used. Those 

 with thin walls, or containing much cartilage, birds and am- 

 phibians, require little pressure, while mammals, in general, 

 can receive much higher. The pressures which I have found 

 to work best vary between 28 and 36 cm. 



The hardening fluid used is Perenyi's, in which the eye is 

 allowed to remain twenty-four hours, when it is changed to 

 70 per cent, alcohol. 



In making changes of liquids, great care should be taken 

 that no air get into the eye, and that all the former liquid is 



