46 Proceedings of the Royal Physical Society. - 
which, as a vale, are plentiful enough—is rather the determina- 
tion of the species. To critically examine thousands of these 
minute organisms is a task requiring not only patience, but 
a considerable amount of time, because it is often absolutely 
necessary to dissect the specimens in order to determine, not 
only specific, but, also, generic differences. To simply crush 
the animal under a cover-glass, and take the risk of finding 
one or more of the appendages in a favourable position, is, to 
say the least of it, a clumsy and unsatisfactory method. No 
doubt, to dissect, for example, a Copepod, perhaps the 
thirtieth to the fiftieth of an inch in length, limb from limb, 
in consecutive order, so as to ascertain the exact relative 
position of each member, and thus be enabled to make a correct 
comparison of the one with the other, requires some practice 
and dexterity, yet only in this way can a reliable knowledge 
of the structure and relationship of the parts be acquired. 
But, though the difficulty of such a procedure be apparently 
great, it is quite surmountable—my son, Mr Andrew Scott, 
to whom I am much indebted for help of this kind in pre- 
paring material for the present paper, is often able to prepare 
a complete series of appendages from a single Copepod, viz., 
anterior and posterior antenne, mandibles, maxille, anterior 
and posterior foot-jaws, and the five pairs of thoracic feet, and 
this has often permitted a satisfactory discrimination to be 
made, which would otherwise have been well-nigh impossible. 
Next session I hope to be able to prepare an account of 
the Cladocera of the district, when I shall, probably, notice 
any species belonging to the other groups which may have 
previously escaped observation. 
THE OSTRACODA. 
I propose, in the first place, to deal with the Ostracoda of 
the area. 2 
It will be understood that the district limits are the same 
as described in my previous paper, and in Mr Evans’s memoir 
on the Mammalha in the Proceedings of the Royal Physical 
Society, published in 1892. 
At a meeting of‘the Royal Physical Society, held on the 
22nd of January 1890, I had the privilege of exhibiting a 
