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two slender, calcareous, transverse bars, one behind and one in front of 
the articular foramen for the maxillipeds. These bars, which end blindly, 
form the remains of the calcareous sternite of the first thoracic somite 
which has evidently lost its rigid connection with the dorsal arch or tergite, 
including the styloid calcification. The pair of posterior bars is movably 
articulated with the sternite of the second thoracic somite. 
Immediately in front of the anterior of these two bars and rigidly 
connected to the keel is a stronger and more important calcification, the 
alar bar, which runs for some distance transversely, to end by curving 
forward just medial to the styloid calcification, with which it forms a 
movable articulation. Neglecting the pair of slender bars belonging to 
the first thoracic somite, one might say that the calcareous maxillo-sternal 
framework is cruciform, the keel and the pair of alar bars forming the four 
limbs of a cross. The two membranous bands which intervene between 
the three foramina for the mandibles and maxillse may be described as 
stretching across the two anterior quadrants of this cross. 
We have now seen that the maxillo-sternal framework, with which are 
connected the paragnaths, the maxillae, and the maxillipeds, is at every 
point movably united to the surrounding parts. Near the mouth especially, 
where it is joined to the surrounding skeleton by long membranous bands, 
the framework is capable of a considerable range of upward and downward 
movement, which will no doubt come into play in the process of feeding. 
We may safely assume that a similar mechanism is present in all isopods. 
I have already had occasion to point out — Tait (1917, I) — that the oedema 
produced by immersion of Ligia in distilled water causes the paragnaths 
to protrude, an effect which could occur only if the skeleton carrying the 
paragnaths is movable. 
Reference has already been made to certain ventral endophragmal 
structures within the cavity of the cephalon. Being rigidly connected to 
the maxillo-sternal framework, these structures participate in all its 
movements. 
The Ventral Endophragmal Skeleton, which might also be considered 
as part of the maxillo-sternal framework, has been but little studied in 
isopods, Lloyd’s account of it in Bathynomus being the most complete. It 
consists in the main of the structures named “ sternal ahe ” by Lloyd, but 
also of two paired rods which spring dorsally from the keel of the maxillo- 
sternal framework. 
When exposed by dissection from behind the “ sternal alee ” of Glypto- 
notus appear as two smooth, pear-shaped objects, which, lying transversely 
on the floor of the cephalosome, meet medially by means of their pointed 
