180 CRUSTACEA—-EUCARIDA—DECAPODA CHAP. 
appendages characteristic of the Zoaea, namely, the first and 
second antennae, mandibles, first and second maxillae, and two 
pairs of biramous swimming maxillipedes and small third maxilli- 
pedes. In the Metazoaea (B), as in the Anomura generally, 
the third maxillipedes develop into biramous swimming organs, 
a thing they never do in the Brachyura, and the rudiments of 
the thoracic segments put in a first appearance. The abdominal 
segments are already fully formed in the Zoaea stage, so that 
here as inall other Zoaeas, the order of development from in front 
backwards is disturbed by the precocious differentiation of the 
abdominal segments. The next stage is the “ Glaucothoe” (Fig. 
123, C), which corresponds to the Megalopa of Brachyura (Fig. 
125,p.185). It differs from the adult Hermit-crab in the perfect 
symmetry of its body, the segmented abdomen, and the presence 
of five pairs of normal biramous pleopods. At this stage, which 
lasts four or five days, it resembles closely a little Galatheid. 
The asymmetry of the adult (Fig. 125, D) is now imposed upon 
this larva by the migration of the liver, gonads, and green glands 
into the abdomen, and by the shifting of the posterior lobes of . 
the liver on to the left side of the intestine, which is displaced 
dorsally and to the right. The gonad les entirely on the left 
side. The pleopods of the right side now degenerate, more 
completely in the male than in the female, and this degeneration 
is not completed until the little crab has found a shell and 
lived in it for some time. If a shell is withheld from it, the 
degeneration of the pleopods is much retarded, so that although 
the Hermit-crab assumes its asymmetry without the stimulus of 
the spiral shell, yet this stimulus is necessary for the normal 
completion of the later stages. 
Fam. 1. Pylochelidae.——The abdomen is macrurous and 
symmetrical, with all the limbs present. Pylocheles (Fig. 118, 
p. aie): 
Fam. 2. Paguridae—The abdomen is asymmetrical, with 
some of the limbs lost. The antennal scale is well developed, 
and the flagella of the first antennae end in a filament. 
Sub-Fam. 1. Eupagurinae.—The third maxillipedes are wide 
apart at the base, and the right chelipedes are much larger than 
the left. Parapagurus from deep-sea, Hupagurus from temperate, 
especially north temperate seas. Pylopagurus. 
Sub-Fam. 2. Pagurinae.—The third maxillipedes are approxi- 
