263 
1916-17.] Experiments and Observations on Crustacea. 
in front of the head, along which line the “ hands ” can be arranged in 
regular series, those of the posterior gnathopods being outermost. The 
lateral stretch of this last pair of limbs just corresponds with that of the 
antennary flagella, and is considerably less than that of the anterior pair 
of perseopods, which have also a greater forward reach. 
It is possible that the gnathopods work in association with tactile 
impressions derived from the antennary flagella. Owing to the backward 
current caused by the pleopods, “ olfactory ” stimuli will tend to reach the 
antennules from in front, not as in a crab from behind — cf. Bethe (1897) — 
so that the animal will approach its food or other desired object head on. 
The flexural arrangements of the gnathopods, the provision of setse on a 
limited (ventral) region of the limb, and the fact that the thorax is capable 
of ventriflexion chiefly in this region, suggest that food is gathered or 
secured under the body, the animal bestriding or settling down upon its 
prey. In any case, it is plain that these prehensile limbs are used not so 
much for reaching outwards as for manipulating portions of food already 
in the vicinity of the mouth region. 
The slenderness of the basipodites and the shortness of the merum and 
carpus are correlated with a feeble development of the basipodal condyles. 
The coxo-basal articulation of the long walking legs with their well- 
developed basipodal condyles is designed to resist a much greater bending 
moment. This slighter build of the gnathopods would in turn indicate 
that any living prey taken by the animal is small and incapable of 
powerful defence. 
The Person. 
Most of the spirit specimens show a certain amount of ventriflexion of 
the body, especially in the fore and mid part of the perseon. The animal 
can be extended until each lateral border forms a straight line, and all the 
females with full brood-pouch are thus fully extended. Dorsiflexion is 
prevented by abutting of the posterior border of each thoracic tergite 
against the pair of sculptured triangles on the succeeding tergite. The 
possibility of lateral flexion is all but absent. 
A slight amount of flexion occurs between the more anterior segments 
of the pleon. Between pleon and perseon a movement of ventriflexion of 
some 10 degrees is permitted; so also at each of the joints between the first 
and second, the fifth and sixth, and the sixth and seventh (“ free ”) thoracic 
segments. Between the second and third, above all between the third and 
fourth , where an abrupt change in the direction of the limbs occurs, and 
between the fourth and fifth segments, the amount of movement is greater. 
