289 
1916-17.] Experiments and Observations on Crustacea. 
have noted that this appendage in Glyptonotus, if not in all similar isopods, 
is peculiarly difficult to disarticulate, in spite of the fact that the basal 
segment in question is very narrow and the corresponding articular 
foramen in the sternal region exceptionally wide — cf. Hansen (1903, p. 22). 
The point of articulation is situated on the lower border of the alar plate 
between the two inferior pterygoid processes. 
It remains to comment upon the morphological significance of the 
ventral endophragmal skeleton. Lloyd has shown that in Bathynomus 
d 
Fig. 19. — Dissection of interior of “ cephalosome” of Glyptonotus. To show alar plates and 
pharyngeal processes. x 2J. 
The cephalosome has been opened from the dorsum, more freely on the left side 
than on the right. The ventral appendages on the left side had been removed, those 
on the right side being left in situ. 
a , chitinous anterior part of pharyngeal process ; b , articular foramen for left 
mandible ; c, alar plate ; d, pharynx ; e, triangular calcareous part of pharyngeal 
process. 
It will be observed that the left alar plate is attached (to the transverse alar bar) 
only by the inferodateral pterygoid process. On the right side this arrangement is 
not so plain because the basal segment of the first maxilla (left in situ) blocks the 
gap below the infero-medial pterygoid process. 
it gives origin to muscles for the foregut and for the post-mandibular 
oral appendages. It seems to be a rule in the anatomy of Glyptonotus 
that the muscles which move the appendages on the body never arise 
from the sternite, but always from the tergite of the corresponding somite 
(this we observe throughout the mesosome and metasome and also in the 
mandibular somite). We have seen that no tergite corresponding to the 
maxillary somites can be recognised on the dorsal aspect of the cephalon, 
while the lateral part of the first thoracic tergite is so greatly reduced as 
to be quite unsuited for any effective muscular attachment. In so far as 
it gives attachment to the muscles of the post-mandibular oral appendages 
VOL. xxxvn. 19 
