Hatching in Aquatic Invertebrates, IX and X — DAVIS 
381 
emergence from the second membrane was by 
the struggles of the animal. Naylor (op. cit.) 
observed that the originally spherical egg be- 
came ovoid after a period of development, and 
that this was followed by the rupture of the egg 
membrane. There was a growth from 0.7 -mm 
diameter in the spherical egg to an embryo 1.2 
mm long. This embryo was still enclosed in an 
"embryonic membrane.” After appendages ap- 
peared in the developing embryo, this mem- 
brane also ruptured. 
In the present study only a single egg mem- 
brane was observed, but the inability of the 
embryos to continue living normally outside of 
the brood pouch, combined with the rapidity of 
movement of the parent animals and the opaque- 
ness of their bodies, may have led to a second 
membrane being overlooked. In the earliest 
stages observed there was no sign of more than 
one membrane; the fact that this one membrane 
lay rather loosely around the embryo does not 
suggest that an outer membrane had been 
sloughed off earlier. 
Summary 
Eggs at various stages of development, and 
hatched young, were taken from the brood 
pouches of Cirolana sp. There was approximately 
a doubling of the size of the eggs from time of 
oviposition to hatching, and the young increased 
in size even more after hatching. It remains 
unclear whether the mother secretes a nutritive 
substance into the brood pouch. Hatching itself 
was accompanied by, and partly caused by a 
sudden and rapid increase of volume of the 
embryo, evidently through a rapid uptake of 
water across the body surface. The stretched egg 
membrane, however, was burst by squirming 
action of the embryo. 
X. HATCHING IN THE FRESH-WATER SHRIMP, 
Potimirim glabra (Kingsley) 
( M ACRURA, ATYIDAE ) 
Several small shrimps were obtained from 
their shelter beneath rocks in a small stream 
(Rio Chiquileco ) , near Mizata, Departamento 
de La Libertad, El Salvador on July 23, 1962. 
They were found not more than 20-30 m from 
the ocean beach, but the water in which they 
0.3 MM 
FIG. 3. Potimirim glabra. The young within the egg 
shortly before hatching. The telson passes anteriorly 
in front of the head, to terminate dorsally over the 
yolk mass. 
lived was fully fresh (though probably subject 
to salt-water contamination during storms). One 
of the shrimps was ovigerous and was returned 
to the laboratory for closer study. The shrimp 
was identified as Potimirim glabra, and the de- 
termination nas been confirmed by Prof. Dr. L. 
B. Holthuis of the Rijksmuseum van Natuur- 
lijke Historie, Leiden, Netherlands. Evidently 
the species has been reported only twice before, 
by Kingsley (1878) from the west coast of 
Nicaragua, and by Holthuis ( 1954^, b) from 
the Rio Jiboa in El Salvador, about 60 km east 
of the present find. 
When the specimen was captured the eggs 
were at a very early stage of development, but 
the shrimp and its eggs lived well in fresh water 
in the laboratory. Five days later the eggs were 
far advanced, for the eyes were conspicuous, the 
hearts were beating (the rate of the heart beat 
varied in the different specimens), and there 
were vigorous intestinal movements. Occasion- 
ally there was a sudden twitch of the body. The 
average size of seven eggs was 500 /x X 300/x 
(they varied little in their dimensions). 
Within the egg (Fig. 3) the lengthy young 
were coiled into an oval. The first two abdominal 
segments lay more or less along the same axis as 
the cephalothorax, but the rest of the abdomen 
folded under so that most of the segments lay 
ventral to the cephalothorax and its appendages. 
The furca was folded over the head, terminating 
