196 
CRUSTACEA. 
size from the head backwards, and the whole embryo covers but 
about a third of the visible portion of the yelk. Subsequently, 
the 5 pairs of legs increase in size, and are doubled on themselves, 
while the mandibles remain very small, and 2 pairs of gills 
make their appearance. At a little later period, about the 
middle of embryonic life, the embryo throws off an embryonic 
skin (Nauplius-skin ) . Still later, the claws are developed, the 
heart appears, the abdominal part of the dorsal portion grows 
broader, with the segments more distinct. Just before hatching, 
the cephalothorax spreads out, the 2 eyes and the pair of ocelli 
are distinct, the 6 segments of the cephalothorax can, with care, 
be distinguished, the 9 abdominal segments are most clearly 
defined, but only a rudimentary spine has appeared on the coxal 
joint, corresponding to the numerous teeth in after life, and the 
whole embryo bears a very near resemblance to certain genera 
of Trilobites, as Trinucleus and Asaphus. In about 6 weeks from 
the time the eggs are laid, the embryo hatches, the segments are 
obliterated, the abdominal spine is very rudimentary, forming 
the 9th segment. The young animal swims briskly up and 
down the receptacle in which it is placed, skimming about on 
its back by flapping the gills, not bending the body. At the 
succeeding moult, between 3 and 4 weeks after hatching, the 
abdominal spine becomes ensiform, and about thrice as long as 
broad. A second moult occurs about 4 weeks afterwards. 
This author also discusses the morphology of Limulus (Proc. 
Bost. Soc. N. H. Oct. 1870, and Am. Nat. iv. pp. 754-756) ; he 
regards the anterior part of the shield as cephalothorax, and 
the posterior as abdomen — features which distinguish it from all 
recent adult Cfustac^a^ but agreeing with the Zoea-stage of some 
of them and with the Trilobites, 
Lockwood has observed the habits (feeding, spawning, and moulting) of 
Limulus polyphemus^ and compares it morphologically with Etirypterus and 
Pterygotus (Trilobites). Am. Nat. iv. pp. 257-273, pi. 3. 
CIRRIPEDIA. 
PELTOGASTRIDiE. 
Saceulina. Anderson (P. Z. S. 1871, p. 144) notes the occurrence in the 
Andaman Islands, Bay of Bengal, on Thalmnita crenata, of a species appa- 
rently not distinct from that foimd in Europe, 
ARANEIFORMIA. 
Pycnogonid^. 
Nymphm pumilio^ sp. n., G^ube, JB. schles. Ges. xviii. p. 85, St. Malo ; 
the hinder pair of palpi without denticulated spines. 
Phoxichilus Icevts, sp. n., id. ibid, and Mittheil. &c. pp. 31 & 60, pi. 1. fig. 1, 
St. Malo. 
