6 
wide range in size is probably due to their long 
breeding season which allows considerable size 
variation in each year class. Mature specimens 
have either gravid ovaries, eggs attached to the 
pleopods, or both. The anatomical changes and 
signs of a mature female are as follows: ( 1 ) the 
fourth abdominal segment is as wide as or wider 
than the third segment in the smaller mature 
specimens, while the fourth and fifth segments 
are wider than the third segment in older 
females; (2) the sixth abdominal segment is 
wider than the second; ( 3 ) the lateral "hair” on 
the sixth and/or seventh segment is equal to 
the length of the third abdominal segment; (4) 
the lock mechanism is lacking; and ( 5 ) the ab- 
dominal groove in the thorax is shallower and 
broader than in immature stages. 
An attempt to analyze the maturity of males 
of this species and of the genus Lophopanopeus 
also met with little success. In both cases, how- 
ever, the intromittent organs were fully de- 
veloped when the male had reached a size 
somewhat smaller than the minimal size (11.5 
mm.) of a mature female. 
Lophopanopeus l. leucomanus and L. bellus 
diegensis: These species were studied independ- 
ently but the data obtained were so similar that 
both will be discussed together. Sexual dimor- 
phism is evident when the female reaches a size 
of 4.5 millimeters. This genus evidently matures 
more quickly in these latitudes than do the 
other genera, for ovigerous females having a 
carapace width of only 8.5 to 9.0 millimeters 
are common. This fact, together with the fact 
that this genus has the longest breeding season, 
explains in part its extensive northerly range. 
Immature females have the following charac- 
teristics: (1) the third abdominal segment is 
wider than any other; (2) the lateral "hair” on 
the sixth segment is one-half or less the total 
length of the third abdominal segment; ( 3 ) the 
pleopods are underdeveloped; and (4) the lock 
mechanism is always present. 
Mature females change in the following way: 
(1) the fourth abdominal segment is as wide 
or wider than the third segment; (2) the 
lateral "hairs” on the last two abdominal seg- 
ments equal the length of the third segment; 
(3) the pleopods are fully developed; and (4) 
the lock mechanism is absent. 
PACIFIC SCIENCE, Vol. XIV, January I960 
Internal and External Genitalia 
The anatomical features of the genitalia are 
the same for the three genera studied, although 
there are some minor variations in shape and 
size of such parts as the male intromittent or- 
gans. The genitalia of Cycloxanthops novemden- 
tatus will be presented as a representative type 
of the other genera in this study. 
The internal genitalia of the male (Fig. 1, A) 
consist of the testes, which are dorsal to the 
liver mass and which join medially over the pos- 
terior portion of the stomach. From the testes 
arise two tightly coiled ducts which are the 
glandular portion of the vasa deferentia and 
which secrete a fluid which aids in the conduc- 
tion of sperm. From these coils, the vasa defer- 
entia pass posteriorly, leave the visceral area, and 
terminate in the coxae of the fifth pair of 
pereiopods. 
The first (Fig. 2, A) and second abdominal 
appendages are modified to transfer sperm to 
FIG. 1. Internal genitalia: A, Internal genitalia of 
a male Cycloxanthops novemdentatus; B, internal gen- 
italia of a female Cycloxanthops novemdentatus; fe- 
male genitalia, longitudinal view. EP, external papilla; 
G, glandular portion of the vas deferens; H, heart; 
IN, intestine; OV, ovary; S, spermatheca; ST, stomach; 
T, testes; V, vulvae; VD, vas deferens. 
