172 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
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plunges downward toward the flexor muscles and during the last 
part of the glaucothoe period, pierces these. Its further develop¬ 
ment could not be followed, as it was impossible to interpret the 
blood vessels through sections of the adolescent stages, owing to the 
twist of the abdomen and consequent confusion of landmarks. But 
it is obvious that this new vessel is to be identified with b' of the adult 
crab’s arteries and that b of the adult system is the superior abdom¬ 
inal. This latter artery swings to the left with the completion of 
the shift of the livers and as the displacement is usually accompanied 
by the suppression of the right segmental artery of the second seg¬ 
ment distal to the origin of U , the latter quickly assumes the adult 
relations and appears to arise directly from the superior abdominal, 
b. Occasionally, however, this segmental vessel will persist in mature 
glaucothoe and even into the sixth stage. The fate of the other 
segmental vessels is uncertain. The four posterior pairs can be 
identified in very mature glaucothoe and occasionally in sixth stage 
larvae. Their presence in the latter stage suggests that they may 
persist in the adult crab, but whether this is actually the case or not 
could not be determined. The anterior pleopods of the adult cer¬ 
tainly receive blood from branches of the superior abdominal 
(Bouvier, ’ 91 ). But on the other hand at this time this vessel does 
not extend to the rear of the abdomen and the uropods are supplied 
by the inframuscular branch of //. 
We have no data with regard to the abdominal arteries of anv 
Pagurid outside of the genus Eupagurus and whether the peculiar 
abdominal blood system of this genus is generally distributed among 
the members of the group is not known. In case it is not generally 
present, it might furnish a valuable criterion of relationship. Among 
other Decapods the artery most nearly analogous to b' occurs in 
Gebia deltura (Bouvier, ’ 90 ) . This vessel, however, arises directly 
from the superior abdominal in the fifth segment and such a poste¬ 
rior position appears to me effectually to militate against regarding 
it as homologous with the Eupagurid artery, b r . The development 
of the latter suggests rather that it originated either as a new 
structure, or, more likely, as an enlargement of some minor branch 
of the segmental artery of the second segment, when the gradual 
suppression of the ventral abdominal artery necessitated a more per¬ 
fect connection between the dorsal arterial trunk and the ventral 
region of the body. Once introduced, the branch has usurped many 
