212 BULLETIN OF THE 



elsewhere sends down irregular cone-shaped masses, which penetrate 

 and become lost in the underlying connective tissue, thus firmly uniting 

 the two layers. Over the vesicle, however, these processes are wholly 

 wanting, the under surface of the epithelial layer being even, and 

 sharply limited from the connective tissue. These processes are espe- 

 cially well developed immediately beyond the margin of the disk of 

 the vesicle, where they carry the cells of the epidermal layer (e'drmj) 

 considerably deeper than their general t level. The connective tissue 

 between the vesicle and the epidermal layer is composed of fibres con- 

 siderably finer and looser than those found in other places, and, further- 

 more, the fibres are here disposed at various angles to the surface of the 

 skin, whereas elsewhere they are approximately parallel to this surface 

 (con't. tisJ). Pigment, which is found in great abundance in the skin in 

 all other regions of the body, is always entirely absent here. It will 

 thus be noticed that each of the tissues over the vesicle is considerably 

 more penetrable to light than are the corresponding ones elsewhere. 

 The connective-tissue fibres immediately around the vesicle are arranged 

 concentrically to its surface, and are, especially in the proximal two- 

 thirds of their extent, considerably finer and closer than elsewhere. 

 A kind of capsule for the vesicle is thus formed, and it is this alone 

 which separates it from the cranial cavity. The fibres of a string of 

 tissue extending from the distal end of the epiphysis can be traced, 

 though with some uncertainty, to this capsule, but I find no indication 

 of their passing through it, or even entering it, though I have given 

 special attention to this point. 



The internal surface of the cranial wall in the region of the vesicle 

 presents a depression, which is much less marked, however, than a cor- 

 responding one in P. coronata, to be referred to hereafter.- Running- 

 through the connective tissue at the bottom of this depression, and 

 hence, near the deep surface of the vesicle, are found a number of blood- 

 vessels of considerable size and well filled with blood corpuscles (va. sng.). 

 The vesicle itself is elliptical in sagittal section, the major axis, 258 jx 

 long in the specimen figured, having the direction of the long axis of 

 the head. In transverse section it is slightly elongated dorso-ventrally, 

 and measures in this axis 171 yu,. 



The cavity in sagittal section shows a triangular outline, the base of 

 the triangle being on the dorsal or lens side. From this outline in the 

 sagittal section the form gradually changes to that of an ellipse in 

 the last sections on each side that cut the cavity ; so that the form of 

 the cavity is approximately that of a broad, flat cone, the base directed 



