No. 2.] COMPOUND EYES OF ANNEUDS. 291 



ment between the separate lenses, and regarded as eyes by 

 Langerhans, who emphasizes the fact that both these species 

 live in transparent tubes. The tube is transparent in Ehlers' 

 species also, but whether these organs are eyes or glands, he 

 regards as not determined yet. 



Finally, Brunotte (9) applied modern methods of technique to 

 the study of these compound eyes in a species of Branchiomma. 

 The eye is here at the tip of the branchia, variable in size, 

 spheroidal except for a colorless furrow on one side, where it 

 does not surround the skeletal axis of the branchia, and is 

 covered by the usual unmodified branchial cuticle. The eye is 

 composed of numerous separate eyes or elements, each a pyra- 

 mid embedded in pigment, with the broad base next the cuticle, 

 the attenuated apex continuous with the nucleated filaments of 

 the branchial nerve. In the base, next the cuticle, is a sphe- 

 roidal, generally homogeneous lens that stains darkly and may 

 be reticulated in some preparations. 



Next this lens is a clear, cup-shaped cavity, sharply set off 

 from the rest of the eye, and containing a nucleus. In the 

 elongated central part of each eye element is a series of trans- 

 verse disks or lamellae, alternatingly clear and more opaque, 

 but not visible in balsam. A second nucleus is found in the 

 eye between this last lamellated "striated spindle" and the 

 first-mentioned outer nucleus. The whole element is thus to 

 be regarded as made up of two cells, an inner or central optic 

 cell and an outer or peripheral, lentigerous cell. No pigment 

 occurs in either of the above two cells, but is found in many 

 small, attenuated, surrounding cells, arranged in circles at dif- 

 ferent levels along the outside of the above apparatus, and 

 each having a nucleus, as seen when depigmented in strong 

 nitric acid. 



The eye is thus two-layered and the visual cells are non- 

 pigmented. Illustrations of these peculiar eyes and comparisons 

 with those of Arthropods are given in a later paper (10), but 

 these may be considered in the final part of this article. 



The last notice of such compound eyes that has come under 

 my notice is that of Beddard (11), who figures a somewhat 

 mushroom-shaped eye borne upon a stalk projecting from the 

 inner face, near the tip, of the branchia of Branchiomma inter- 

 medium, a new species from the Mergui Archipelago. 



