316 BULLETIN OF THE 
The posterior border of the telson (Pl. IT. Fig. 15, f) now but slightly 
exceeds the anterior end in width. It is deeply concave, and furnished 
with but eight long sete. The spaces between the long sete contain two 
very small sete; those in the median interspace are longer than the rest. 
It appears from my notes that on the 8th of August, 1878, a speci- 
men in the stage described above as the third moulted in one of my 
aquaria, and then appeared in a shape differing in one respect from that 
which I have just described as the fourth larval stage. Besides the 
acquirement of the sixth pair of swimming-feet, the seventh pair were 
developed in this specimen as biramose, clearly segmented, setiferous 
appendages (Pl. II. Fig. 14), but very small in size compared with the 
sixth and preceding pairs. The last pair of thoracic limbs were simple, 
sac-like organs. This early development of the seventh pair of swim- 
ming-feet I regard as premature ; in the normal course of development 
it is anticipated by the eighth pair, as will appear presently.* 
Fifth Larval Stage (Pl. 111, Figs. 4 = 13). — This stage was reared from 
the fourth stage in one of my jars. The most important structural ad- 
vance upon the preceding stage consists in the full development of the 
hindmost pair of thoracic appendages. The flagellum of the second pair 
of antenne has increased in length, and the long terminal segment shows 
a faint indication of division into four segments. There is a short spine 
(Fig. 4, II, sp.) on the outer side of the distal end of the posterior 
antennée, which becomes larger in later stages of the development. This 
spine is more highly developed in the larve of Paguride, and represents 
the enormously developed spinous process of the second pair of antenne 
so frequently found in the zoëæ of the Brachyura, From the exuvie of 
one individual I obtained for the first time the complete structure of tlie 
mandible (Fig. 7, 777). It is composed of two branches, as in the adult, 
but the anterior branch, instead of presenting a molar crown, as in the 
full-grown animal (Pl IV. Fig. 19), ends in multidenticulate incisor 
edge. "This branch is concealed beneath the fleshy labrum, and henco 
escaped detection in the earlier stages, 
The chela of the fourth pair of swimming-feet is more perfectly formed 
than before, the penultimate segment being much enlarged, with its 
internal angle produced as far as the middle of the terminal segment 
* J find among some larve which I preserved in alcohol one specimen with five 
pairs of natatory appendages (in this agreeing with the third stage above described), 
but in every other respect agreeing with the fourth stage. Behind the last pair of 
swimming-feet are the double, sac-like rudiments of the two following pairs. Length, 
4mm. 
