192 MEAD. [VoL. XIV. 
II. DESCRIPTIVE. 
(a) Collection and Preparation of Material. 
The observations recorded in the following pages were made 
upon the eggs of Cheptopterus pergamentaceus Cuvier, pro- 
cured at the Marine Biological Laboratory, Woods Holl, Mass., 
during the summers of 1894, 1896, and 1897. 
These extraordinary annelids are found below low-water 
mark in leathery tubes. The latter are U-shaped, ten to 
fifteen inches long, about an inch in diameter in the widest 
part, and are buried beneath the mud except half an inch at 
either end. After being removed from the tubes the animals 
may be kept alive for a few days in an aquarium; they are 
quite helpless in their new environment, and usually lie on 
their side, keeping up continuously the rhythmical respiratory 
movement of their wing-like body-folds, which, under natural 
conditions, would serve to create currents of water through the 
tubes. When disturbed at night, they emit a phosphorescent 
light, apparently dependent upon a secretion from epidermal 
glands, for the water in which they have been kept becomes 
itself slightly phosphorescent. 
The sexes are readily distinguished, the body-wall being 
nearly transparent and the posterior segments distended with 
eggs or spermatozoa. The large parapodia hold the sexual 
products, and any number may be cut off without injury 
to the worm. The eggs may be fertilized at any time 
during the day or night and will develop normally, provided 
the sperm is added within a few hours after they have been 
removed from the ovaries. This is true of every individual 
collected during the months of July and August, and indicates 
that the eggs are probably carried in the body for many days after 
they are perfectly mature and ready to be fertilized. If the 
eggs are kept in sea-water for half an hour or more and not 
fertilized, all except the smaller ovarian eggs are found to have 
the first maturation-spindle well formed, in its definitive posi- 
tion, and always in the same stage of development, 2.¢., the 
metaphase or equatorial-plate stage. But, if the eggs are ex- 
