RESPIRATORY ORGANS IN DEOAPODOUS CRUSTACEA. 457 
Sars. Boas inferred from this that the gill was therefore quite 
a different structure to that of the Euphausidse, but Professor 
Claus (in the paper I have already referred to) has shown that 
it would be absurd on account of mere difference of position 
to call the two gills separate structures. The development of 
the Lophogastridse has not as yet ever been thoroughly made 
out, but it seems probable that the position of the gills on the 
arthrodial membrane is due to the fact of their developing at 
a later period than in the Euphausidse after the full formation 
of the appendage, and to the subsequent sinking of the coxo- 
podite into the body wall. This also seems likely from the 
fact that the Lophogastridae have no longer a free metamor- 
phosis, and therefore it is of no advantage to the embryo to 
have its gills developed early. Each of these gills is compound, 
consisting of either three (Lophogaster) or four (Gnathophausia) 
distinct lobes springing from the same point. If the arthrodial 
membrane to which they are attached were to be stretched we 
can easily see how these four lobes would be pulled apart, and 
would thus assume the appearance of separate gills. The 
variability of the boundaries of the arthrodial membrane is 
shown by Professor Claus in the development of one of the 
Brachvurous larvae to which I shall afterwards refer (p. 461). 
Of the lobes of the gill three are covered in by the carapace, 
and the fourth projects freely beneath the trunk, meeting its 
fellow in the middle line (fig. 10). 
Let us now see what has become of the epipodite during this 
development. In the Euphausidae, in all the forms mentioned 
by Sars (of which there are six or seven genera), this is entirely 
absent, although Sars, and also Boas, regards the gill as re- 
presenting the epipodite. Only in one form mentioned by 
Sars (Bentheuphausia), which has a very complicated gill, it is 
difficult to say whether epipodite is or is not present as well as 
gill. Since, in the higher Crustacea, we have in so many 
instances the epipodite present as well as, and perfectly distinct 
from, the gill, it seems probable that this vascular outgrowth, 
although in outward form very closely resembling an epipodite, 
is really to be regarded as an independent organ rather repre- 
