Biology of Pachygrapsus crassipes —HIATT 
199 
as separated individuals. The actual copulatory 
position is, therefore, assumed with rapidity. 
The infrequent observations of copulation, when 
compared with the vast number of hours of 
observation both in the laboratory and field, 
would indicate that copulation occurred chiefly 
at night or that it persists for a very brief inter¬ 
val. The present data strongly favor the former 
supposition. 
TABLE 8 
Size and Age at Adulthood (Determined 
by Presence of Spermatozoa) of 50 Male P . 
crassipes Taken on June 13, 1941. 
BREADTH 
(MM.) 
NUMBER 
OF CRABS 
AGE* 
(months) 
SPERMA¬ 
TOZOA 
22.0-26.0 
6 
15-16 
many 
20.0-21.9 
8 
14 
many 
16.0-19.9 
7 
11-14 
many 
14.0-15.9 
8 
10-11 
few to many 
12.0-13.9 
8 
7-10 
none to few 
10.0-11.9 
7 
5-6 
none to few 
8.0-9.9 
6 
4-5 
none 
* Ages were determined from Figure 10, page 167. 
Several close-up observations of copulating 
pairs have disclosed a constant positional pat¬ 
tern. Contrary to all descriptions of the copu¬ 
latory act in other Brachyura, in this species 
it is the male which lies on its carapace below 
the female. The second, third, and fourth perei- 
opods of the male are placed between those of 
the female, and the dactyls are hooked over 
the lateral edge of her carapace. The fifth perei- 
opods of the male are looped around the pos¬ 
terior side of the corresponding appendages of 
the female, and the dactyls are hooked at the 
posterolateral edges of her carapace. The am¬ 
bulatory appendages of the male, therefore, 
serve to grasp the female. The chelae are gen¬ 
erally flexed in their normal folded position; 
however, at intervals those of the male are 
employed to grasp the female, and occasionally 
are utilized for protection from the thrusts of 
the female’s chelae directed toward the male’s 
oral area. The abdomen of the female com¬ 
pletely covers that of the male, that of the latter 
being below the abdomen of the female. In 
this position the ventral surfaces of each mem¬ 
ber are contiguous, and the action of the penes 
is difficult to observe. 
Although difficult to follow from above or 
below, impregnation was observed upon two 
occasions from the side. The abdomen of the 
male moved slightly forward and back with the 
penes inserted only a short distance into the 
vulvae. 
Although the infrequent observations of 
copulation in this animal suggest brevity, the 
data secured for P. crassipes indicate extreme 
variability and comparatively long duration. 
In one field observation, in which impregnation 
appeared successful, the pair were in coitu for 45 
minutes. Upon another occasion captive crabs 
were observed in copulation for 6 minutes (the 
onset was unnoticed) prior to separation. After 
the separation the male partially flexed and 
extended its abdomen arhythmically and, when¬ 
ever the male approached its mate, the abdomen 
oscillated with increased tempo. In addition, 
this male repeatedly elevated and depressed 
its right cheliped. It seemed apparent that im¬ 
pregnation had not been completed. A copula¬ 
tory act by another captive pair occurred and 
lasted for 15 minutes. When the crabs sep¬ 
arated, they stood with their flexed chelae con¬ 
tiguous and the abdomens of both moved brisk¬ 
ly; however, copulation was not resumed. Copu¬ 
lation by a third pair lasted for 20 minutes. 
The animals frequently moved about the aqua¬ 
rium while the female supported the suspended 
male. Another pair were in coitu for 5 minutes 
prior to separation. Several hours later the pair 
was again observed in copulation which per¬ 
sisted 4 minutes. It is highly significant to note 
that all the females mentioned above, com¬ 
parable to most accounts in the literature, were 
in stage A lt while the males were in C 3 or 
above. On the other hand, Broekhuysen (1941) 
indicated that copulation in C. punctatus 
occurred only between hard-shelled crabs. 
Some anomalous copulatory behavior observed 
both in captive and wild crabs aided in apprais- 
