744 William Patten 



ration of the liypodermìc cells, x; at the summit of the papilla is a speci- 

 aliy large tuft of sense hairs. The ciiticula over the summit of the Oph- 

 thalmie fohl was unusually thick. Cam. Hart. obj. 7, oc. II. 

 Fig. 7. Sectioii through the mantle edge of P. ojìercularis, showing the develop- 

 mentof a teutacle, t, betwoen the Ophthalmie fold and the eye; s.pa., is a 

 pigmented sense hair papilla Avhich occupies the usuai position of the 

 young cyes ; x , ono of the problematical cells which occur at regulär in- 

 tervals along the summit of the Ophthalmie fold. 

 Fig. 8. A pigmented sense hair papilla whosc sense cells, «/.e .are being transform- 



ed luto ganglionic ones. 

 Fig. 9. Section through the mantle edge, uear the hinge, otÌAyoiiìig P.o^Hrcularis. 

 The ciliated Ophthalmie fold hasbeen divided by the tentacle, t, into two 

 parts; «, thickened ciliated folds on the branchial wall of the mantle. 

 Fig. lo. Section, atright angles to the edge of the mantle, through analmost com- 

 plete eye of P. imsio. The vitreous network is much thicker than in the 

 adult, and the two layers of the argentea stili contain a few flattened nu- 

 clei. At ar, are many remarkable fibres, the remnauts of the primitive 

 nerve fibres, fig. 4 n.f. , which penetrate the sclerotica and pass up to the 

 rods. Cam. Hart. obj. 5, oc. IV. ; tube out 1 in. 

 Fig. 11. Section through the Ophthalmie fold and eye papilla of a young P. ojtcr- 

 ciilaris. At hy. the hypodermis, by proliferation, has givcn rise to the 

 hypodermic core, which, later, will give rìse to the optic vesicle; some 

 of the cells, (j.c. are separating themselves from the others to form gang- 

 lionic cells, which always remain connected with the core by means of 

 nervo fibres. Cam. H. obj. 7, oc. IV. 

 Fig. 12. Section through the Ophthalmie fold oi P. pusio; the proliferation of the 

 hypodermic cells has given rise to a solid core of cells; mesodermìc cells 

 have grown round the core forming the connective tissue capsule, et. e. 

 Some of the cells of the core have wandered into the underlying tissues 

 to form ganglionic cells, one of which is represented, f/.c. Cam. H.ob).7, 

 oc. IV. 

 Fig. 13. Section, near the hinge, of the mantle edge ofayoungP. opercularis, 

 showing the remarkable modification of the Ophthalmie fold into a thick- 

 walled rìdge, the cilia having disappeared. Cam. H. obj. 5, oc. IV. 

 Fig. 14. Section of the Ophthalmie fold of a very young P. opercularis (1 mm long); 

 the summit of the fold is imperfectly forked and is covered with un- 

 usually long cilia ; at the base , is a very young optic papilla. The nuclei 

 are scanty at y,while at hy.c. they are two or three deep, showing the first 

 stagesjn the formation of an hypodermic core. Cam. H. obj. 7, oc. IV. 

 Fig. 1-5. Section through a highly developed fold, similar to those marked a in 

 figs. 1, 3 and 9, from the branchial wall of the mantle of a young (2 mm) 

 P. o])crcidarìs. The cilia are extraordinarily long and their proximal ends 

 are continued as fine lines a long way into the protoplasm. Cam. H. obj. 

 5, oc. IV. 

 Fig. 15a- A more magnificd section of the peripheral part of the thickening, show- 

 ing the thick and beaded cuticula, containing the pores for the passage 

 of the cilia. 

 Fig. Iti. Section through the Ophthalmie fold of a young P. opercularis. Showing 

 an optic papilla Mith a half formed hypodermic core from which some 



