1916-17.] Experiments and Observations on Crustacea. 
69 
VI. — Experiments and Observations on Crustacea : Part III. 
Limb-Flexures and Limb-Taxis in the Peracarida. By John 
Tait, M.D., D.Sc. (From the Laboratory of Physiology, Edinburgh 
University.) Communicated by Professor Sir E. A. Schafer. 
(MS. received September 1, 1916. Read November 20, 1916.) 
In order to obtain light on the functional heredity of the limbs of Ligia 
it was found necessary to consult the morphological papers of Boas (1883), 
of Hansen (1893), and of Caiman (1904), on the classification of the 
Malacostraca, along with monographs and other records devoted to 
smaller groups. The result has been somewhat curious, for an investi- 
gation originally undertaken from a physiological standpoint has become 
semi-morphological. Finding that some of the accepted views with regard 
to the flexures of the limbs of Crustacea do not throw sufficient light on 
the case of Ligia, I have made an attempt, starting with Ligia, to restate 
the question of limb-flexion as met with in the Peracarida. From paucity 
of comparative knowledge such an essay cannot hope to have any finality. 
It is rather the belief that the morphologists have not said the last word 
on the subject that has induced me, tentatively and with second-hand 
resources, to enter upon a difficult task in an unfamiliar field. 
For convenience I have arranged my remarks under sections, com- 
mencing with a description of the walking limbs of Ligia, which contains 
detail not given by Hewitt (1907) in his monograph on the animal. This 
first section will likewise serve as part introduction to a subsequent 
communication which will deal with gait. 
The Walking Legs of Ligia. 
Seven in number on each side, the walking limbs form a remarkably 
uniform series, as in all the Oniscoidea. Each limb consists of six movable 
segments (basipodite to dactylopodite). From before backwards they 
gradually increase in length, the seventh in order being nearly twice as 
long as the first. 
Basipodites . — The largest and most powerful segment of each limb is 
the basipodite, which, arising laterally, is, in the position of flexion, 
directed medially. The successive basipodites increase slightly in length 
from before backwards. In flexion — the position of rest — they lie in 
grooves along the ventral soft tissue of the thorax, each pair posterior to 
