Feeding Habits of Hippa - — Matthews 
385 
the tenth drop of Physalia solution was in- 
troduced before the crabs stirred. As in E the 
controls emerged before the tenth drop of 
Physalia solution was introduced. Microscopic 
examination of the antennules of operative 
and control crabs revealed only sand grains 
enmeshed in the setae and the contents of the 
dissected digestive systems again revealed un- 
altered nematocysts but no microorganisms. 
G. Of the 50 sand crabs collected for this 
experiment about the same number (30) sur- 
vived the operative shock of removal of eyes 
and antennules as survived the removal of eyes 
and antennae. These exhibited about the same 
activities as those described in F. There was 
the same confusion, the same colliding one 
with another, the same running around the 
tank and the same submerging without any 
special orientation. Again 3 to 5 minutes 
elapsed after the tenth drop of Physalia solu- 
tion was introduced before the crabs emerged. 
No difference, either in time or in magnitude 
of response, was discernible between blinded 
sand crabs with antennae removed and blinded 
sand crabs with antennules removed. As in 
E the controls emerged before the tenth drop 
of Physalia solution was introduced. Micro- 
scopic examination of the antennae of test and 
control crabs revealed only sand grains, and 
the contents of the dissected digestive sys- 
tems revealed only unaltered nematocysts. 
H. After the tenth drop of the colored 
Physalia solution reached the 12 sand crabs 
that had survived the removal of eyes, an- 
tennae and antennules 15 to 21 minutes was 
required before any visible response occurred. 
As in previous experiments the controls 
emerged before the tenth drop of Physalia 
solution was introduced. For the most part 
the test crabs merely broke the surface of the 
sand, appeared to "tread water” momentarily, 
and then settled below the surface. As pre- 
viously mentioned, these crabs were dead on 
arrival at the laboratory and their digestive 
systems were not examined. No microorgan- 
isms were present on the controls. 
DISCUSSION 
Gregarious sand crabs lie submerged in 
large "beds” with only eyes and antennules 
projecting above the shifting, wave-washed 
sand. In Emerita , for example, exceedingly 
long antennae, folded behind the maxillipeds 
(vide Weymouth and Richardson, 1912, pi. 
1, fig. 7), are thrust out anterolaterally as 
waves recede; thus characteristic V-shaped 
ripples, which mark the "bed’s” location, are 
formed (vide MacGinitie and MacGinitie, 
1949, figs. 145-146, p. 302). However, Ha- 
waii’s only hippid (Edmondson, 1946, p. 
265), has exceedingly short antennae (vide 
Dana, 1855, Atlas: Crustacea, pi, 25, fig. 7a), 
thus the characteristic V-shaped ripples result 
from water striking the antennules, rather 
than the antennae. 
Weymouth and Richardson (op. cit. p. 11) 
conclude that microorganisms found in the 
stomach of Emerita analoga were strained 
from waves and that antennae and mouth 
parts "are remarkably adapted to this form of 
feeding, and unfitted for any other.” In 
Emerita analoga the function of sensory an- 
tennal pits in feeding appears negligible as 
highly diversified materials generally reported 
from their stomachs (diatoms, radiolarians, 
foraminifera, spicules, one-celled algae and 
sand) are "about what would be obtained by 
unselective straining of the water along shore” 
(Weymouth and Richardson, op. cit., p. 9). 
In contrast to the unselective antennal 
straining of Emerita, feeding by H. pacifica, 
at least during high surf, is selective as evi- 
denced by their acceptance of Physalia and 
their rejection of algae, shrimp, and Velella. 
Moreover, this selectivity is attributed, in part 
at least, to some sense other than sight for, 
although all experimental solutions probably 
appeared similar to the crabs, the Physalia 
solution alone evoked visible responses. Yet, 
so long as the eyes remained intact, selection 
based on some chemical sense (vide Mon- 
crieff, 1946, p. 152; Ramsay, 1952, p. 85; and 
Prosser et al., 1950, p. 453) although a strong 
