28 CTENOPHORES OF THE. ATLANTIC COAST OF NORTH AMERICA 
ugal (abaxial) edges lie along a deep groove which extends down the 
sides of the body adjacent to the oral lappets, from the mouth to the 
level of the apical sense-organ. The auricle side of this groove is ciliated, 
while the opposite side is provided with numerous short, simple tentacles. 
which lie immediately over 4 lateral tubes that diverge from the para- 
gastric vessels. This long, deep furrow at once distinguishes Muemiopsis 
from Bolinopsis. Both sides of the long, slit-like mouth are bordered 
with a row of short, simple tentacles which are continuous with those 
of the deep, lateral furrows. The central tentacle on each side is longer 
than the others and gives rise to lateral filaments. The 4 rows of ciliated 
combs leading to the auricles are only about half as long as the 4 rows. 
extending down the outer surface of the oral lobes. The combs are small, 
but numerous. The stomodzum is long and narrow and is provided with. 
cilia at its aboral end. The axial funnel-tube is only about one-fifteenth 
as long as the stomodeum. The peripheral canals are of fine caliber, 
and the meridional ventral canals give rise to simple windings in the 
oral lappets. The oral lappets are provided with delicate transverse 
and longitudinal muscle fibers. The lappets are of no appreciable aid. 
in swimming, this being performed almost entirely by the action of the 
combs of cilia. The creature is almost colorless, being of a slightly milky 
translucent hue. The ciliated combs sparkle with brilliant iridescence 
by day and glow with an intense green light when the animal is disturbed. 
at night. The gelatinous substance of this ctenophore is often infested 
by a pink colored, worm-shaped, parasitic, larval actinian (Edwardsia). 
The development (figs. 20-41, plates 6 and 7) has been studied by 
A. Agassiz. As in other ctenophore, the animal is hermaphroditic, 
and the egg is spherical and is enveloped by a thin, structureless mem-. 
brane which is widely separated from the surface of the egg (see fig. 20, 
plate 6). The deeper portions of the egg are filled with large, slightly, 
refractive masses of food-yolk, between which there is a delicate reticulum 
of protoplasm. The superficial layer of the egg is composed of finely 
granular protoplasm. The segmentation is total but unequal. The 
first two cleavage planes are meridional and cut in the direction of the 
longitudinal axis of the future ctenophore from the animal to the vege- 
tative pole. The third cleavage is also meridional, but shifted to one 
side and the other, and it divides the embryo into 8 cells, 4 large central. 
and 4 small lateral cells, the 4 small cells being at the extremity of the 
longer axis of the embryo, which becomes the tentacular axis of the 
future ctenophore. The 4 small, laterally placed cells then migrate 
upward toward the animal pole. The next cleavage is equatorial and cuts. 
off 8 small, uppermost cells from 8 large, yolk-laden macromeres. The 
small cells then begin to divide rapidly and to extend downward, cover- 
ing over the 8 macromeres, thus beginning to form a gastrula by epibole. 
Meanwhile the cleavage cavity remains open, so that the cells form a. 
Ting surrounding a central space which extends as an opening from the 
vegetative to the animal pole. The animal pole corresponds to the aboral: 
apex of the future animal. The small micromeres which are to form the 
ectoderm envelop the macromeres, forming a cap which overlies them 
(figs. 22 to 24, plate 6). Before the macromeres are inclosed, however, 
they divide, giving rise to a number of small cells, some of which form. 
