GENERAL MORPHOLOGY, GEOGRAPHICAL DISTRIBUTION. Crust. 9 
lence is applied to the neighbouring distal part of the foot, by reflexive 
movement. Arch. Biol. iii. pp. 235-240. 
C. Matzdorff has published some very interesting observations on the 
variability of colour in Idotea tricuspidata (Desh.), enumerating and 
figuring a number of varieties in colour, and stating that they are not 
confined to sex. He further states that the same individual changes its 
colour by expansion or contraction of dark brown chromatophorous cells, 
and that its general coloration becomes in that way lighter or darker if 
confined in a light or dark coloured vessel. Individuals creeping near the 
tip of Algae or Hydroids on their natural dwelling-places are usually more 
pale-coloured ; those remaining on the ground rather dark, and by prefer- 
ence females. After the extirpation of both eyes, the animals do not 
change colour. Diss. inaug. (title supra), also in Jen. Z. Nat. xvi. 
pp. 1-58. 
Adaptation of colour in Carcinus mamas ; Carrington & Lovett, 
Zool. 1882, pp. 12-14. 
Incidental observations concerning the feeding- of some Crabs and 
Paguridce, by A. E. Verrill, Am. J. Sci. (3) xxiv. pp. 360 & 447. 
R. Kossmann, Zool. Anz. 1882, p. 60, gives a tabular review of the. 
parasitical Crustacea , as follows : — 
I. Diosmotici : not themselves digesting, but taking nourishing fluids 
direct from the body of their host. Rhizocephala. 
II. Sedentarii : themselves digesting, but in the adult state not able to 
change their host. Bopyridce, Entoniscidce , Cryptoniscidce , and 
part of Copepoda. 
ill. Vagantes : digesting, and changing the host also in adult state. 
Cymothoidce , Argulus , and part of Copepoda. 
Note on the commensalism of Pagurus and Adamsia ; H. Eisig, Das 
Ausland, lv. pp. 681- 686. 
Alplieus cumatularum, Gebia deflexifrons, and an undescribed Cymothoid, 
as commensals of Comatula ; Has well, P. Linn. Soc. N. S. W. vi. p. 763. 
Geographical Distribution. 
1 . Land and Fresh-water Crustacea. 
F. A. Forel recapitulates the principal features of the pelagic fauna 
of fresh-water lakes, enumerating the species of Crustacea which are most 
characteristic of it. These are widely distributed over the European 
fresh-water lakes from Sweden to Italy, and are all well adapted for 
swimming, and of pellucid colour, feeding either on swimming Algce or 
R n animal prey ; they perform daily migrations, being during night at the 
surface, and descending during the day as far down as 100 and even 150 
metres. He thinks that most of them may be derived from allied forms 
which inhabit the littoral regions of lakes, but that, once adapted to a 
pelagic life, their eggs may be transferred by water-birds to other lakes, 
which will account for their wide geographical distribution, and their 
occurrence in lakes of rather recent origin. Leptodora and BythotrCphes 
alone have no near relation to littoral fresh-water species, and for these 
