Hatching in Aquatic Invertebrates, IX and X — Davis 
383 
caused by an osmotic swelling of the inner mem- 
brane. The swelling continued until the outer 
membranes were sloughed off and until the 
inner membrane burst and liberated the young. 
Herrick (1911) has described some aspects of 
hatching in the American lobster, Homarus 
americanus. He observed that an outer mem- 
brane burst first, and that an inner membrane, 
which was attached to the outer one, remained 
surrounding the hatching larva. When the inner 
membrane was shed the larva emerged, but 
must then molt before it was free-swimming. 
The bursting of the outer egg membrane in 
Potimirim glabra could not have been associated 
with the presence of any hatching spines or 
egg bursters. The only structures so placed on 
the embryo that they might have acted in this 
manner were the anteriorly directed lateral 
spines on the carapace, but if these had caused 
the bursting of the outer membrane they would 
also have done so to the inner membrane, which 
remained intact. It was clear that the bursting 
was caused by considerable pressure from 
within, and it is postulated that this occurred by 
the osmotic uptake of water through the inner 
membrane, although perhaps the embryo itself 
took up water also, as indicated by the fact 
that there was no space between the embryo 
and the inner membrane at the time that the 
outer membrane broke. That such a space ap- 
peared later, however, suggests that osmotic 
water was being taken in through the mem- 
brane. Estimates of possible further increase in 
size of the embryo itself at this time, however, 
were not possible because of the manner in 
which it loosened up its compact folds within 
the inner membrane. This made accurate com- 
parative measurements impracticable. 
The fact that the outer membrane invariably 
burst over the cephalic region suggests a weak- 
ened line of dehiscence there, although before 
bursting no such line was visible with the high 
power of a compound microscope. 
Hence, in Potimirim glabra the hatching 
process is a combination of osmotic bursting of 
an outer membrane and active mechanical exit 
by the animal through the inner membrane. 
Evidently no enzymatic action is involved, unless 
there is an enzymatically caused change in the 
permeability of the inner membrane at hatching 
time. 
Summary 
Potimirim glabra hatched through the osmotic 
swelling of an inner egg membrane; the pressure 
caused the rupture of the outer membrane, 
which then was sloughed off by continued swell- 
ing of the inner one. Final hatching from the 
inner membrane was accomplished by the strug- 
gles of the young shrimp, which broke the mem- 
brane over the head by action of its telson, then 
tore the membrane further by straightening out 
its highly coiled body. 
REFERENCES 
Andrews, E. A. 1904. Breeding habits of the 
crayfish. Amer. Nat. 38 (447 ): 165-206. 
1907. The young of the crayfishes As- 
tacus and Cambarus. Smithson. Contr. Knowl. 
35:1-79. 
Burkenroad, Martin D. 1947. Reproductive 
activities of decapod Crustacea. Amer. Nat. 
81 (800): 392-398. 
Churchill, E. P. 1917-1918. The life history 
of the blue crab. Bull. U.S. Bur. Fish. 36:93— 
128, 9 pis. 
Davis, Charles C 1959. Osmotic hatching in 
the eggs of some fresh-water copepods. Biol. 
Bull. 116(1): 15-29. 
1961. A study of the hatching process 
in aquatic invertebrates, II. Hatching in Ra- 
natra fusca P. Beauvois (Hemiptera, Nepi- 
dae). Trans. Amer. Micr. Soc. 80(2) :230- 
234. 
1964. Ibid., VII. Observations on hatch- 
ing in Notonecta melaena Kirkaldy (Hemip- 
tera, Notonectidae) and on Ranatra absona. 
D. and DeC. (Hemiptera, Nepidae). VIII. 
The hatching process of Amnicola hydro- 
bioides (Ancey) ( Prosobranchia, Hydrobii- 
dae) . Hydrobiologia 23 ( 1-2 ) : 253-266. 
Ellis, Robert J. 1961. A life history study of 
Asellus intermedins Forbes. Trans. Amer. 
Micr. Soc. 80(1) : 80-102. 
Forsman, Bror. 1944. Beobachtungen fiber 
Jaera albifrons Leach an der schwedischen 
Westkfiste. Ark. Zool. 3 5 A ( 1 1 ) : 1—33, 1 pi. 
