486 Baron Osten Sacken on the differences between 
iu.j fig. Ij and iv., figs. 5-7), the outspread fringes of the 
four processes, when under water, " form a cup, filled 
with air, and from this air can be taken into the 
spiracle/' 
All these appliances are adapted for enabling the larva 
to breathe the gaseous air through spiracles, or to get 
it under water, either by means of an artificial cup, 
which holds a bubble, or else by means of branchial 
appendages. It is well known now that such a com- 
bination of breathing appliances in the same species is of 
rather common occurrence among aquatic larvae of 
Diptera. 
We have, hitherto, examined the dorsal side of the 
four larvae and discovered resemblances which evidently 
depend upon similar conditions of life in running waters. 
The ventral side of the larvae of Mariiina, as well as their 
pupa-state show considerable, and, as to their usefulness, 
as yet unexplained differences from the larva and pupa of 
P. canescens. 
The ventral side of the Ifaruina-lsirvdd is described 
thus (compare above, Dr. Miiller^s letterpress) : "The 
three species are provided with a longitudinal row of six 
suctorial discs, the last of which occupies the penultimate 
ventral segment (Tab. x., fig. 2). Concerning the 
structure of these discs, I can only refer to the figures (6 
and 7), as, at present, I have no other descriptive data 
at hand.^"' 
There is nothing like these suctorial discs in the larva 
of P. canescens (Tab. iii., fig. 2). The ventral side is 
described as follows : " The ventral surface is more 
uniformly covered with tubercles and set^. A pair of 
small and distinct plates, which appear to be more solid 
than the neighbouring integument, defend the middle 
annulus of most of the abdominal segments on the 
ventral side, lying within the shield." (Miall, p. 143 
at top.) 
Much greater is the difference between the pupa of P. 
canescens and that of the South American Maruinx, 
The former is very much like most of the papae of the 
Nematocera, especially the Tipulidse (Tab. iii., fig. 3) ; it 
has a fiexible abdomen, the segments of which are 
provided with circles of hooks, and some larger spines, 
for locomotion. The pupa of M. pilosella (Tab. xi., fig. 
8) is shield-like, flat, adherent, and, apparently, unfit for 
