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1916-17.] Experiments and Observations on Crustacea. 
separated ; those for the maxillipeds are closely approximated in the middle 
line ; so too are the articular foramina for the second maxillse ; from this 
point forwards the foramina diverge like the limbs of a V, those for the 
mandibles being once again widely separated. In other words, of the 
primitive cephalic somites only the one corresponding to the mandibles 
shows indubitable evidence of participation in the general lateral expansion 
of the body. Consequently we might suppose that by the strong lateral 
development of this particular primitive somite the more posterior cephalic 
somites have been crowded out from the lateral region, and thus their 
sternites left, as it were, floating. A similar movable maxillo-sternal frame- 
work is obviously present in Bathynomns — see Milne Edwards and 
Bouvier (1902, pi. iv, fig. 9). 
Attention may be drawn to a kind of antero-posterior symmetry in 
the arrangement of the sternal articular foramina for the appendages of 
Glyptonotus. We have seen that the appendages of the mesosome are all 
widely separated. As we pass from mesosome to metasome the double 
longitudinal row of sternal articular foramina suddenly becomes drawn 
together medially, gradually to diverge farther back, attaining greatest 
divergence at the uropods. Similarly, as we pass from mesosome to 
cephalosome proper, the series of sternal articular foramina are suddenly 
approximated towards the middle line, to diverge anteriorly, attaining 
greatest divergence at the mandibles. One might also note that the 
cephalon is, as it were, pushed backwards into an excavation in the front of 
the thorax, the pleon being similarly received into an excavation in the 
hinder part of the thorax. A transverse cut carried across between the 
two anterior points of the farthest forward thoracic epimera would pass 
through the mouth ; a similar cut at the level of the posterior points of 
the farthest back thoracic epimera would pass through the anus. The oral 
and the pleopodal are very closely packed as compared with the thoracic 
appendages. 
Having obtained a general idea of the skeleton of the cephalosome, 
we pass to a more detailed consideration of some of the parts. We may 
designate the lateral triangular expansions of the first and of the second 
intracephalosomic septum as the “ first (triangular) lamina ” and the 
“ second (triangular) lamina ” respectively ; the thoracic somites will be 
numbered according to their position in the primitive series of eight ; 
and some new descriptive terms will be introduced. 
The First Thoracic Somite . — Examination of the interior of the cephalo- 
some having made plain the position of this somite, it is easy to trace its 
boundaries on the external dorsal aspect. Its greatest (antero-posterior) 
