1890.] Zoology. 373 
Entozoa of Marine Fishes.—Professor Edwin Linton has pub- 
lished a first paper on these forms, which, though included in the Fish 
Commission Report for 1886, did not appear until 1889. Professor 
Linton has spent several summers at Wood’s Holl collecting the inter- 
nal parasites of fishes. In the present paper he confines himself to 
the Cestods and Acanthocephala. Seventeen species in all are enumer- 
ated, of which ten are regarded as new, while three new genera are 
made in the paper. The general distribution of these parasites is sum- 
marized thus by Mr. Linton: Cestoid entozoa in the adult or strobile 
condition were found in great numbers in the alimentary tracts of all 
the Selachians examined. Encysted forms of the Cestoidea are for the 
most part confined to the Teleostei, and are found in greatest abund- 
ance in the sub-mucous coat of the stomach and intestine, although 
not infrequently met with in the peritoneum, liver, spleen, ovaries, etc. 
A Two-Tailed Earth-Worm.—Some time ago one of my stu- 
dents brought in a specimen of a two-tailed earth-worm. While the 
literature of the subject is not at present accessible to me, I am under 
the impression that no such abnormal form has been reported from the 
United States, although several have been found in other parts of the 
world. When the animal was alive it seemed really two-tailed, the 
parts appearing of equal importance, but in the alcoholic specimen 
one division appears like a lateral branch, and is quite markedly con- 
stricted where it joins the body of the worm. Branches of the intestine 
and ventral nerve cord pass to both divisions, and there are two func- 
tional ani. The alcoholic specimen is 34 mm. long, the ‘ tails” being 
about 12 mm. long.—C. Dwicut Marsu, Ripon College. 
Compound Eyes of Arthropods.—Mr. S. Watase has pre- 
sented (Studies, Biol. Lab., Johns Hopkins, IV., No. 6) an extremely 
ingenious view of the morphology of the compound arthropod eye. 
The compound eye is formed by the vegetative repetition of the visual 
unit or ommatidium. In Serolis each ommatidium constists of two 
corneagen cells, which secrete on their outer (free) surface the chitinous 
cornea. Beneath these come two other cells (vitrelle=retinophore), 
which secrete on the surfaces toward the axis of the ommatidium the 
chitinous crystalline cone, which, according to Watase, is purely di- 
optric, and has no connection with the optic nerve fibres. Beneath the 
vitrellæ are the retinule, cells which have their deeper ends in commu- 
nication with the optic nerve, while their surfaces toward the axis of 
the ommatidium secrete a chitinous rod or rhabdomere. This structure 
is therefore to be regarded as a pit of ectoderm the cells of which, like 
