86 Proceedings of the Royal Society of Edinburgh. [Sess. 
Stenetrium, or rather the species antillense figured in Hansen’s paper, 
might have either tanaidacean or isopodan taxis ; within the group 
of Parasellidge, Jcera certainly has isopodan taxis, while some other 
forms are doubtful. Thus, figures of Desmosoma and of Ischno.soma, 
in which the basipodites occupy a position impossible in the case of 
Ligia, suggest tanaidacean taxis. Similarly, Munnopsis typica appears 
to have tanaidacean taxis, but Sars’ (1899) figure, pi. lviii, in which, 
by exception, the ventral aspect appears, clearly shows the presence 
of isopodan taxis. It may be that all the Asellota have primitively 
an isopodan limb-taxis ; on the other hand, some of them may not. 
Judging by this group there is no proof whatever that our principle 
is of any particular value for systematic purposes. In face of this 
unsatisfactory evidence, it would be useless to urge that the principle 
is based on an examination of wide groups of animal, including orders 
beyond the limits of the Isopoda. 
Let us take the Valvifera, another homogeneous group. Though 
not recently revised it contains, according to the statement in Caiman’s 
(1909) invaluable book, six families — Idoteidge, Chgetiliidge, Pseud- 
idoteidge, Holognathidse, and Arcturidse. The limb-taxis criterion makes 
a sharp line of division between the last family and the first five, 
which are all idotean in general aspect and have isopodan taxis. Thus 
the old separation of the Arcturidse from the Idoteidge — see Miers (1883) — 
is brought more into prominence than the other subdivisions. Here 
I am again unable to say whether our criterion is of any special value. 
Sars’ group Flabellifera is admittedly more heterogeneous than 
Valvifera. According to the test by limb-taxis, there is a clear line of 
division between the Gnathiidge and Anthuridge on the one hand and 
the remaining families of the sub-order on the other. Caiman, not 
specially concerned with limb-taxis, remarks : “ The Gnathiidge . . . are 
an aberrant family whose relation to the more normal Flabellifera is 
not clear, and the same may perhaps be said of the Anthuridge.” 
The taxis in the Epicaridea is isopodan. This may be compared 
with the statement, “ the Epicaridea are closely related to some of the 
Flabellifera, the systematic value of the modifications due to parasitism 
having been here as elsewhere somewhat overestimated.” 
On the whole the amount of light we get by application of our new 
morphological criterion is problematical. Nor do we get much help in 
establishing a satisfactory phylogeny by considering that tanaidacean 
taxis is widespread and isopodan limited to its own order. 
Physiological. — So soon as we consider the matter in its functional 
