290 Proceedings of the Royal Society of Edinburgh. [Sess. 
the ventral endophragmal skeleton fulfils the function of tergites. Conse- 
quently one would correlate the presence of this skeleton with the absence 
of tergites : which suggestion in turn raises its own problems. 
The Oral Appendages. 
The oral appendages of Crustacea possess a special importance for the 
systematist, and in the case of Glyptonotus they have been carefully 
described. Our knowledge of the function of these appendages is, how- 
ever, very meagre, so that I have ventured to set down some additional 
details as a guide to any worker with access to living material — -in which 
connection it may be pointed out that few Crustacea seem better adapted 
for experimental work along this line than Glyptonotus, with its large 
size and readily accessible mouth parts. 
Hansen (1893) has sought to advance our knowledge of the morphology 
of these appendages by attempting to establish detailed homologies between 
them. Thus he says : “ In order to understand the structure of the maxillae 
in the Malacostraca we must commence with the maxillipeds.” It is un- 
necessary to expound the assumption that underlies such a statement. In 
a recondite matter of this kind the quest of homologies is apt to resolve 
itself, as indeed it usually does, into mere reasoning in a circle. 
The Mandibles articulate with the cephalosome by a simple hinge (an 
anterior and a posterior articulatory pivot projecting from each mandible 
fit into corresponding sockets in the heavy skeleton of the cephalosome). 
The posterior of the two sockets is situated within the mandibular articular 
foramen ; the anterior lies in front of the foramen at the base of the 
labrum. Each mandible may be said to consist of a proximal body, semi- 
cylindrical in shape, and of a distal biting process, which is carried in a 
smooth curve (its neck) from the body forwards, medial wards, and ventral- 
wards to end in the biting surface, which includes a molar and an incisor 
process. 
On the body we recognise the following important parts: (1) the two- 
articulatory pivots; (2) a large medially placed, cylindroid maxillary 
polished surface, which rubs against the antero-lateral aspect of the hard 
lateral lobe of the first maxilla ; (3) a much smaller, posteriorly placed, 
flattened, styloid polished surface, which rubs against the styloid calcifica- 
tion ; (4) a polished groove medially situated at the join of the body with 
the neck and burnished by friction against the lateral border of the 
paragnath ; (5) a postero-lateral abductor process for attachment of the 
abductor muscle. Attached by a band of connective tissue to the free 
edge of the appendage, just dorsal to the maxillary polished surface, is a 
