333 ;^. WA^'ASL'. 



Figs. 47-56. Consecutive series of transverse sections of the com- 

 pound eye of Limulns at tlie beginning of tlie lateral invagina- 

 tions. Fig. 47, No. 1; Fig. 48, No. 3; (the section No. 2 is essentially 

 the same as No. 3). Fig. 49, No. 4; Fig. 50, No. 5 ; Fig. 51, No. 6; 

 Fig. 53, No. 7; Fig. 53, No. 8; Fig. 54, No. 9; Fig. 55, No. 10; 

 Fig. 56, No. 11. The lateral invaginations become distinctly marked 

 at Fig. 49, No. 4, and fuse in the median Hue at Fig. 54, No. 9, 

 forming the median fold (»«./). 



Tlate XX.XlV.—LimuIus. 



Figs. 57-64 show the condition of the lateral and median 

 invaginations of the compound eye in the stage shown in Fig. 41, 

 PI. XXXIl. 



Fig. 57. In this the plane of section passes through the anterior 

 part of the eye, and the dorsal invagination («/./) of the compound 

 eye is distinctly shown. The skin is thrown into folds; into the 

 concave lumen of the fold a slightly thickened portion of the cuticle 

 fits, forming the rudiment of the lens-cone (C); and the cells 

 forming the walls of the invaginated fold form the beginning of the 

 ommatidium. 



Fig. 58 shows the widest portion of the eye in tiiis stage; the 

 beginning of the ventral invagination (r./) is distinctly recognizable. 

 The dorsal fold {cl.f) is very large. Four distinct ommatidia are 

 formed in this section, each depression being accompanied by a 

 slight thickening of the correspondiug portion of the cuticle (C). 

 The basement membrane is very distinctly seen underneath the 

 ocular area and beneath the general ectoderm cells which lie out- 

 side of the ocular area. The action of acid to which the sections 

 were subjected in order to remove the pigment granules has inter- 

 fered with the preservation of the ectodermal cells in those regions, 

 although the thick, refractive basement membrane remains quite 

 distinctly. 



Figs. 59, 60 and 61 show how the lateral invaginations are gradu- 

 ally approaching as we go towards the posterior part of the eye. 

 In Fig. 63 the ilorsal and ventral folds (d.f and v./) meet in the 

 median line, and in Fig. 03 they form a complete tube, the granular, 

 non-pigniented layer coming to the outside and the pigmented cell 

 layer {Fg.c) occupying the deeper part of the tube. The basement 

 membrane (B. M) forms a complete capsule around the tube. The 

 basement membrane which underlies the general ectoderm comes to 



