Eyes ut' Mollusca aud Aitluopods. 743 



Explaiiatiou of tlic Plates. 



Piate 28. 

 On the Development of the Eyes oi Pecten opercularis and Pecten pusio. 



iiffK outer hiyer of argeutcii. Lb. lateral, or ganglionic, brauch of 



«(/'-'. inner » » >, the optic nerve. 



b.h. basal, or axial, brauch of optic n.f. nerve fibrös. 



iitü've. "•'■/• nuclei of the retinophorae. 



b.s. blood siuus. "f- Ophthalmie fold. 



c. cornea. n^>'- "Ptic nerve. 



r.r/. cuticular gland. i'^J' Pife^'n^^»t. 



CMp.v. cavity of optic vesicle. i'^'"' Pseudo-cornea. 



cp.n. circumpallial nerve. '' le ina. 



c.t.c. connective tissue capsule of the ' *" '^' 



„ >.iii. rector muscles of the eye. 



. , . , , , ,, f.o. rete vitrosuui. 



cu. cuticular coverini? ot the shell. , 



° 5. septum. 



ii.c.c. inner row ot gangiiouic cells. ^ 1 . *• 



sc, sclerotica. 



tl.tn. depressor inuscles 01 the eye. , , ,. ... 



^ •' S.C.C, outer layer ot ganglionic cells. 



^- Eye. .s/«./; shell fold of the mantle. 



(f.c. gangiionic cells. s.l. suspensory ligament. 



/ly. hypodennis. s.pa. scnsory papilla. 



hy.c. hypodermis core ofyoung eye. t. tentacle. 



i. iris. tu. tapetum. 



/. lens. V. velum or velar foldof the mantle. 



Fig. 1. Section through thc mantle edge of a young rccten opercularis (2 mm long) 

 in the neighborhood of the hinge. The Ophthalmie fold is not developed 

 in this region; on the side next the branchial cavity, the wall is t rown 

 into several ciliated folds, a, of v?hich the outer is characterized by pecu- 

 liar tufts of cilia over each cell. 



Fig. 2. Section through the median part of the mantle edge of P. opercularis {5 mm 

 long). At the summit of the Ophthalmie fold is a problematical cell x\ 

 at y, is one of the minute transitional and invaginate eyes. 



Fig. 3. Section through the mantle edge, near the hinge, of P. opercularis (2 mm 

 long), showing the thickened folds, a, on the branchial side of the 

 mantle, and the bilobed Ophthalmie fold, o.f. 



Fig. 4. Section through a young eye of P. opercularis, showing the first stages in 

 the development of the optic vesicle, already surrounded by the connec- 

 tive tissue capsule, into the retina, argentea and tapetum. Cam. Hart, 

 obj. 7, oc. IV. tube out. 



Fig. 5. Section through a more advanced eye of P. opercularis, in which are shown 

 the first traces of the lens, /, the thickened retinal layer, r, the inner and 

 outer layers of the argentea, ag^ and ag-, and the tapetum, ta. The iris 

 has made its first appearance as a ring of piginent granules , i. Cam. obj. 

 XX. Leitz, oc. III. 



Fig. 6. Section through the mantle of P. varius, showing a young sensory tentacle, 

 «.^^«,with the rudiments of the tcntacular nerve formed by tlie prolife- 



