A Study of the Hatching Process in Aquatic Invertebrates 
IX. Hatching within the Brood Sac of the Ovoviviparous Isopod, 
Cirolana sp. (Isopoda, Cirolanidae) 
X. Hatching in the Fresh-water Shrimp, Potimirim glabra 
(Kingsley) (Macrura, Atyidae) 
Charles C Davis 1 
Through the kind cooperation of the Institute 
Tropical de Investigaciones Cientificas of the 
Universidad de El Salvador, and through a travel 
grant provided by the Graduate Research Fund 
of Western Reserve University, it was possible 
to continue, in the summer of 1962, a study of 
the hatching processes of aquatic invertebrates 
in the tropical environment of El Salvador, Cen- 
tral America. I wish to express my gratitude to 
the sponsoring agencies for their aid in making 
the study possible. 
Previous publications in the present series are 
listed in Davis (1964). As has been shown in 
these publications, hatching may be achieved by 
the swelling of the embryo (growth or water 
uptake), by mechanical means, by osmosis 
through a nonliving egg membrane, by enzy- 
matic action or by some combination of these 
methods. 
IX. HATCHING WITHIN THE BROOD SAC OF THE 
ovoviviparous isopod, Cirolana sp. 
(ISOPODA, CIROLANIDAE) 
Numerous specimens of Cirolana sp. were 
collected on July 23, 1962, from empty ship- 
worm galleries in pieces of old wood wedged in 
the rocks between the tide marks near the village 
of Mizata, in the eastern portion of El Salvador 
(Departamento de La Libertad). Specimens were 
identified as possibly a new species of Cirolana 
by Dr. H.-E. Gruner, Zoologisches Museum, 
Berlin, and as being close to C. diminuta Men- 
zies (but possibly as a new species) by Dr. 
1 Department of Biology, Western Reserve Univer- 
sity, Cleveland, Ohio. Manuscript received August 13, 
1963. 
Robert J. Menzies, Duke University Marine 
Laboratory, Beaufort, N.C. 2 
Living specimens were returned to the labora- 
tory for study. Many of them contained eggs or 
young in their brood pouches at all stages of 
development. The earlier stages of embryonic 
development were enclosed in definite egg mem- 
branes, but later stages were free in the pouches. 
In Cirolana sp. the brood pouch is so firmly 
enclosed that the eggs and young could be re- 
moved only by disruption of the body of the 
mother. Recently laid eggs removed in this 
fashion (Fig. 1) were ovoid, about 730 /x long 
and 600/x wide. The egg membrane was not 
turgid, and fit rather loosely, leaving a con- 
siderable space between it and the embryo. Later, 
when the young isopod took on more definitive 
form ( Fig. 2 ) , the entire mass increased greatly 
in size so that, although the width decreased 
somewhat to 540ft, the length became 1,350ft. 
At this time the egg membrane had come to fit 
the embryo much more tightly but, as shown in 
the figure, small fluid-filled spaces still occurred 
in front and just behind the head, as well as 
lateral and posterior to the abdominal segments. 
The beating heart could be seen clearly in the 
region between the thorax and the abdomen. 
Just before hatching from the egg membrane, 
all fluid-filled spaces disappeared, and the em- 
bryo increased to an average of 1 ,590/x X 580/x 
(10 measurements), an increase of 2.2 times 
in length.- 
Hatching itself was passive as far as move- 
ments of the appendages of the embryo were 
concerned. Swelling became much more rapid, 
so that the length increased within 15 min 
2 I wish to express my thanks to both of these men 
for their help. 
378 
