MUSEUM OF COMPARATIVE ZOOLOGY. 215 



quite circular, but are never much elongated. In many, though not in 

 all, an exceedingly thin endothelial lining can be seen, and in a few in- 

 stances blood corpuscles are found in the cavities (Plate I. Fig. 4, erCth. 

 va. and cp. sng.). Although none of these cavities were found to extend 

 through more than four or five sections, each 7.5 //, in thickness, and 

 although in no instance was it possible satisfactorily to trace a connec- 

 tion between them and the blood-vessels lying outside the vesicle, it still 

 seems quite certain that they form a network of fine blood-vessels rami- 

 fying through the substance of the retina. Owing to the fact that in some 

 instances no lining membrane to these cavities can be found, and that 

 their outlines are not sharply marked, the possibility of their having been 

 artificially produced by the removal of pigment masses suggests itself; 

 but the definiteness of the outline of many others and their endothelial 

 lining membranes, in which much-flattened nuclei are found, strips this 

 conjecture of its plausibility. If these are really blood-vessels, it might 

 appear that some of them would be seen cut longitudinally ; and while 

 it is true that in many cases focusing shows the cut walls to be very 

 oblique to the plane of the section, still no sure instance of a vessel 

 cut lengthwise has been seen. When, however, one considers the 

 exceeding delicacy of the endothelial lining, and the fact that no differ- 

 ential staining takes place, it does not seem impossible that such sec- 

 tions may exist, and yet escape detection. These cavities have no 

 regularity of arrangement, but are for the most part confined to zones 

 2, 3, and 4. In no instance has one been seen confluent with the 

 cavity of the vesicle. 



These may possibly correspond to what Owsjannikow mentions as 

 having been seen by him in Chamaeleon vulgaris. He says: "Am hin- 

 tern Rande der Retina findet sich an einigen Schnitten das Lumen 

 eines Rohrs, von dem nicht mit Bestimmtheit gesagt werden kann, ob 

 es einem Blutgefasse oder einem anderen Gewebe angehort." (Owsjan- 

 nikow, '88, p. 16.) 



3. The Epiphysis. — Figure 9 (Plate III.) represents a sagittal sec- 

 tion of the epiphysis, and so much of the brain as is necessary to show 

 the relation of the former to the latter. The entire structure, or, more 

 properly, the combination of structures that must be considered at this 

 time, presents the form of a curved cylinder, one end of which is pro- 

 duced into a cone, while the other end has a hopper-shaped excava- 

 tion. In keeping with the usual method of designation, I shall call the 

 whole structure the epiphysis, though, as the sequel will show, it is 

 doubtful if this is justifiable. The excavated end is proximal, the 



