52 Proceedings of the Royal Society of Edinburgh. [Sess. 
and laterally by the indented free border of the branchiostegite. These 
indentations accommodate the coxae of the thoracic legs, while the inter- 
vening apices fit in between ; but, whereas the former (with the exception 
of the concavity from the chela) are in close contact with the chitinous 
portion of the respective coxa, the latter are comparatively loosely applied 
to the soft arthrodial membranes. Thus the cleft may be divided into four 
separate “ inter-coxal ” passages, the first being the space for the coxa of 
the chela and the remaining three those between the apices and the lax 
joint membranes — see fig. 2. 
‘On lifting the branchiostegite and exposing the posterior gills, one 
found them to be touching one another except at their origins, where they 
were distinctly separated by a small gap. It was also easy to note that 
Fig. 2. — Ventral surface of Carcinus, legs removed at coxo-basal joints on 
left side ; coxae themselves partially removed on the right side. 
Semi- diagram matic. 
1-4, indicate the “inter-coxal spaces.” 
the last or 9th gill did not lie perfectly flat on the adjacent epimeron, but 
was slightly arched a short distance from its root. This arching was not 
peculiar to the 9th gill, but occurred in the 8th, 7th, and 6th as well, and 
is in fact mainly due to the flabellum of the third maxillipede. 
Examination of the remaining gills showed that under the 1st gill 
was a large anterior inlet, kept patent by the commencement of the third 
flabellum. This inlet communicates with that under the 9th gill by means 
of a “ tunnel ” formed by the arching of the posterior gills. Leading from 
the anterior inlet but not in direct connection with the sub-branchial cleft, 
another gap was found between the 2nd and 4th gill origins. Besides 
causing this gap, the second maxillipede flabellum is also responsible for 
the arching of the 4th and 5th gills. The 3rd gill, arising as it does from 
the coxopodite of the third maxillipede, helps in the formation of the tunnel 
already described. 
Altogether, therefore, there are five “inter-branchial inlets” — see figs. 
3 and 4. 
