1916— 17. j Experiments and Observations on Crustacea. 297 
carida one pair, members of the Euphausiacea, etc., none at all, is of 
systematic interest, but stands for nothing more. Again, we have only the 
vaguest idea as to the function of the two pairs of maxillae present in all 
Crustacea. In order to understand the relation between different types of 
oral appendicular apparatus it would seem advisable to experiment upon 
some large form which is at the same time sufficiently simple — and 
Crustacea thus doubly qualified are rare. Consequently an experimental 
investigation of the mouth parts of Glyptonotus might greatly help to 
clear up the matter. 
The Midgut. 
It is remarkable that 1 this part of the gut in the spirit-preserved 
specimens is fixed in a much dilated condition, its cavity being consider- 
ably greater than the volume of the contained food, which can be shaken 
about as a compacted cylindrical roll within it. In some examples the 
inner lining shows longitudinal rugae on the ventral aspect, in other cases 
the whole internal wall seems to be stretched smooth. It is hard to 
believe that during life this part of the gut is incapable of contracting on 
the food; if it does so contract, it is not plain how the dilatation has 
occurred, unless it be by shrinkage of the muscles and other structures 
occupying the lateral compartment of the thorax. In one example, whose 
extreme breadth was 49 mm., the width of the midgut was 20 mm., i.e. 
two-fifths of the breadth of the body. 
The midgut, which is fusiform, is drawn to a point at the posterior end, 
which is situated, according to circumstances, opposite the sternite of the 
sixth or seventh of the (true) thoracic somite. Here the alimentary tube is 
greatly narrowed down, without being involuted into the hindgut, as in the 
specimen of Bathynomus examined by Lloyd. In some individuals the 
roll of food material was found to be continuous along this constriction, 
in others the gut at this part was tightly shut down for a distance of 
some millimetres. It is plain that this intermediate short portion between 
midgut and hindgut acts as a sphincter. 
In every case there was a slight want of alignment between the 
posterior end of the midgut and the anterior end of the hindgut, the former 
deviating towards the right, so that the narrow connecting tube formed a 
sigmoid bend. A sigmoid bend with similar direction has been described 
by Collinge (1916) as an abnormality in Idotea linearis. 
The hepatic caeca were too much macerated to permit of examination. 
I failed not only to discover the number of caeca, but even to determine 
their length. 
