200 
Nicholls — Two New Plireatoicids. 
2)rcliensile in P. aatfiniilis, so thnt in this S2)eeies one must su2»]JOse 
the giiatliojjocls to be used in 2>Hiriiig'. It would be of interest to 
know whether in P. australis and other surface-living forms the 
fourth 2)eraeoj>od has siq)erseded the gnathopod in this function or 
is merely auxiliary thereto. 
A com2)arison of the size of the brood in Amphisopus and Phrea- 
loicus is of interest. In P. shepliardi, which reaches according to 
Wayce (I 900 j a length of LOnim., Chilton records that tlie brood x^ouch 
contained a dozen eggs^ while from the 2>oucli of an llnim. specimen 
of A. palustris I have collected more than fifty just emerged larvae. 
In a second case there were counted forty-eight living young and 
one dead. Prom the Ijrood 2)ouch of A. lintoni there were extracted 
thirty-five large embryos. Tliese facts suggest that adatAation to 
sub-ali)ine life has resulted not only in a stunting of the growth^ but 
in a diminution, also, of the rei^roductive ca2)acity. In none of my 
S2)ecimens of P. joyncri or E. kcrshawi do the brood pouches contain 
eggs or embryos, and nothing has been recorded for other members 
of the family. The accommodation of the body to subterranean life 
will 2)ro))ably have restricted still furtlier the number of the off- 
S2>ring. In Hyperocdcsipus, of wliich very few females have been 
taken (2)robably for the reason suggested above in the case of A. 
palustris) , the normal number of eggs is round about four, though 
in one which paired in an acpiarium, seven eggs were seen in the pouch 
Avhen the animal was killed. 
In A. palustris the embryos Avere a full 2 mm. in length at the 
time of their emergence, rvith the six pairs of peraeopoda usual in 
larval Isopoda. The body Avas almost transparent, of a palely broAvn 
tint, and a large j^roportion of the larvae a^jpeared to bear one or 
more of the infesting stalked Infusorian, these having evidently 
sjjread on to the young while still within the brood-^much. The em- 
bryos of A. lintoni Avere more than l^mm. in length Avheii as yet only 
the rudiments of the limbs could be discerned, and it is 2)robable that 
the larvae would be at least twice that length. The tirst antennae 
Avere sliort, consisting of a three jointed peduncle and a slightly 
clubbed flagellum Avitli five Joints, someAvhat closely resembling the 
condition in adult P. australis or P. joy)icri, Avhich might be inter- 
preted as evidence that, in this aijpeiidage, the sub-alpine forms have 
retained very nearly the larval condition. 
After tAventy-four days, the yfuuig died off quite suddenly, per- 
ha 2 >y ai>2)roaching the critical j^criod of the first moult. 
The brood ])ouch is coni])osed of four pairs of lamellae, the 
first (internal to the gnathopods) being unequally bilobed, the 
anterior lobe the smaller and making u]) much of the {interior Avail of 
the 250*^ich. In all of these lamellae then; is a central stouter axis, 
around Avhich is a broad and transparent margin (respiratory ? ), 
