128 PATTEN. [VoL. II. 
through the anterior edge of both these structures—and not 
those shown in Figs. 79-81, which pass through the middle of 
the appendage — will show the continuity of their retinal cells. 
After the stage shown in Fig. 81, I have not been able to detect 
evidence of this continuity, although the vertical furrow contains 
retinal cells up to the very outermost edge of the eye. 
Surface views indicate that the peculiar structures found in 
all the other eyes, such as the median rows of cells and the large 
nucleus, are probably present in the dorsal appendage, although 
imperfectly developed. My failure to detect them in sections 
may be due to the difficulties of observation. 
In longitudinal vertical sections of eye I., the dorsal append- 
age is seen to be somewhat thickened in the middle, the rod- 
bearing ends of the retinal cells converging toward an imagine 
centre some distance above the corneagen. 
The appendage is never sharply limited from the surrounding 
ectoderm; it is less so in the older stages than during the period 
when it is an open cup or newly closed vesicle (Figs. 80 and 
81). The basement membrane is continued without interrup- 
tion from the surrounding ectoderm, over the inner surface of 
the appendage, and this tends to obscure still more the limits 
of the parts in question. 
The retinophorz of the appendage are much like those of the 
other eyes. They are long, spindle-shaped cells with double 
rods, and hence probably contain two nuclei and an axial nerve 
fibre. 
The observations recorded in this paper were made entirely 
upon material collected in a small pool near Milwaukee. In all 
these specimens the appendage was entirely devoid of pigment.} 
In the larve that formed the basis of my preliminary note on 
the ‘Eyes of Acilius,” in the first number of this Journal, and 
which were collected near Boston, Mass., the retinophorz of _ 
the appendage contained large blotches of pigment just below 
the rods. 
Grenacher has described, without figures, the dorsal appen- 
dage in the larva of Acilius sulcata as being pigmented. He 
failed to recognize that it was composed of two distinct 
layers; and while he thought it was in all probability some kind 
1In some of my sections I have noticed, since this was written, mere traces of 
pigment at the base of the rods in the Milwaukee species. 
