292 E. B. Wilson—Polychetous Annelides. 
on the eggs of Arenicola and Clymenella seems of some interest. 
The eggs are small and very numerous, and are embedded in 
transparent gelatinous masses issuing from the mouths of the 
tubes or burrows inhabited by the worms. The egg-masses of 
Arenicola are of great size, being sometimes five or six feet in 
length and from two to four inches in diameter; such a 
must contain several hundred thousand eggs. ‘hose of Cly- 
menella are usually about the size and shape of a pigeon’s egg ; 
the eggs are much fewer and considerably larger than those of 
Arenicola. 
The whole course of development is essentially alike in the 
two forms. No polar globules of constant relation to the yolk 
were observed. The first cleavage divides the egg into two un- 
equal spherules. The second, passing at right angles to the 
first, divides the smaller spherule into two equal parts, and the 
larger into two unequal parts. The third cleavage separates 
from these four blastomeres four much smaller ones at one 
pole of the egg. The latter (micromeres) soon become so dis- 
placed as to alternate with the former (macromeres). The mi- 
cromeres now divide more rapidly than the macromeres which 
anus arises at the posterior end of the embryo. The egg-mem- 
brane is directly converted into the cuticle of the larva. The 
egg exhibits, during segmentation, alternate periods of activity 
and quiescence. 
The embryo acquires two dorsal eye-specks, pra-oral and 
pree-anal belts of cilia and a broad ventral band, and becomes 
a “'Telotrochous” larva which passes directly into the adult. 
The setz develop from before backwards, and those of the 
dorsal ramus appear before those of the ventral. 
The segmentation is closely similar to that of some Oligo- 
cheeta (Huaxes, Tubifex) and resembles also that of the leeches. 
The gastrula stage is not attained by a typical invagination but 
by a down-growth of the ectoderm over the entoderm. 
Beaufort, N. C., July, 1880. 
