32 The American Naturalist. [ January, A 
The cleavage of the eggs is complete but unequal, and results 
in a few large cells full of yolk becoming covered over appar- 
ently by smaller cells containing less yolk. The resulting — 
larve remain for a long time within the egg-sacs, closely — 
crowded together. At an early stage these larve are prob- 
ably about the same as the pear-shaped larva of Leucodora 
figured by Mecaniknow in 1865, and may be regarded as © 
trochospheres much distended by food-yolk. Such a stage is — 
represented from a ventral view in Fig. 12, where the large tri- ~ 
angular mouth lies at the bottom of a ciliated depression of the 
small anterior end, while the main rounded mass is filled with food- 
yolk showing imperfectly the outlines of a few large entoderm ~ 
cells. A ventral ciliated band is present, as well as an imperfect a 
post-oral ring, or rather two lateral ciliated areas, since, as in some — 
other Annelid larvæ, the cilia are absent in the median area, both 
dorsally and ventrally. ; 
Sections of this larva (Fig. 13) show that there is an outer ec- 
todermal layer surrounding the entodermal yolk,—in which latter, — 
however, the cell outlines do not appear,—that there is a paired 
mesoblast, and that the cesophagus ends blindly in the yolk mass. — 
Moreover, sections to one side of the median plane show peculiar, — 
large, ciliated cells, about the mouth, of which there is an espe- 
cially large pair just posterior tothe mouth. One of these is seen , 
in the figure. 
These larva are about .o2 mm. long, and pass gradually into 
a stage with three pairs of seta bundles and a length of .35 mm. 
These latter have four eye spots, an additional band of cilia an- 
terior to the anus, but still a large mass of yolk in the thick 
walls of the digestive tract, surrounded by the body-cavity. fi 
This stage with three pairs of seta bundles is found for a long 
time, though much growth in the size of the body takes place, 
and conspicuous pigment areas appear when the late ! 
form such as shown in Fig. 14 results. The occurrence o 
this phase of larval growth, in which three somites are functiona 
for some time, has been observed in several Annelid larvæ, andis 
Suggestive from its resemblance to the Nauplius condition: 
certain Arthropods. 
ST pF See Mee = ens Se ees Tn Stik Mee ear eae eee 
