BY W J. McKAY. 887 



Fig. 1. — The first stage in the development of the epiphysis of Grammato- 

 jihora muricata. It is seen to be composed of cohimnar cells, and 

 to spring from the junction of the thalamencephalon with the mid 

 brain. 'Ihe slight curve t'n.E., is the first indication of the 

 formation of the secondary vesicle to form the pineal eye. 



Fig. 2. — Pn.E. secondary vesicle springing from the primary evagination. 

 The lower portion of the vesicle rests on the upper part of the 

 roof of the fore-brain. 



Fig. 3. — Transverse but slightly oblique section of same stage as fig. 2. The 

 strands of the coagulable humour are seen in the vesicles. Some 

 of the cells are undergoing karyokinesis. 



Fig. 4. — The pineal eye has become separate from the epiphysis. The epi- 

 dermis is represented by a layer of squames {Cut.), and a layer of 

 cubical cells {R. Mp.). Below this a slight layer of pigment is 

 developing. The pineal eye is seen to be composed of columnar 

 cells. Above is the lens (Le.), below the retina [Rt.) and between 

 the two the optic vesicle {Op. V.). 



Fig. 5. — First stage in the development of Hinulia kcniolata, after the eye is 

 separated from the epiphysis. The lens is composed of two layers 

 of columnar cells with round nuclei, which stain deeply. Below is 

 the retina composed of its several layers, some of which stain 

 deeply, others do not. In the centre is the optic vesicle with humour. 

 The epiphysis is seen to be composed of cells very similar to the 

 lens cells of the eye. Below the eye the blood vessel {B. V.). 



Fig. 6. — Layers of retina : — C.A., the clear area containing nothing else but 

 the cell-processes. This may be the molecular layer. iV""the layer of 

 nuclei, some of which may be seen still to have the remains of a 

 cell around them ; they lie in the layer of connective issue Ct' . 



Fig. 7. — Section of the head of llinulia sp., showing the position of the 

 eye. In front of the eye is seen an evagination very similar to 

 the eye itself. Behind the 63^6 is the second alluded to in the 

 text; it is the end of the epiphysis. The blood vessel runs 

 below the eye. 



