204 ANNULATA. 
CHAPTER XVII. 
ANNULA TA— Continued. 
NEPHROPS. BLATTA. PERIPATUS. EPEIRA. 
I.—NEPHROPS.* 
PHYLUM ANNULATA (p. 237). 
SuB-PHYLUM ARTHROPODA (p. 240). 
CLass CRUSTACEA (p. 241). 
‘he Norway Lobster (JVephrops norvegicus) is a very 
common kind of lobster found, amongst other places, in the 
wapits. Firth of Forth. It is caught in great numbers 
"in the trawl] and is apparently gregarious in its 
habits. It is a ground-feeder and is fond of shell-fish, but 
will eat almost any marine animal of a sufficiently small 
size. It is rather smaller than the common lobster, and 
is at once distinguished by its pale yellow and red colour 
and its more angular outline. 
The body is perfectly plano-symmetric and is encased in 
a hard calcareous exoskeleton. As in the Aznelida, the 
whole body is enveloped in a chitinous cuticle 
secreted by the underlying ectoderm (or epi- 
dermis), but this cuticle is greatly thickened 
over certain areas, and is, in addition, converted into a hard 
plate by the deposition of calcareous matter in the chitin. 
The hard plates are called sc/erites, and the soft cuticular 
parts between them which make movements possible are 
called the arthrodial membranes. 
We can distinguish the body and the appendages, as in 
many Annelida. In the body the largest sclerite is the 
carapace. This rests like a saddle on the anterior 
half (or more) of the body. The front end is 
produced into a sharp rostrum, and on either 
side it hangs down as a lateral branchial plate. The 
branchial plate can be broken off, and the gills are then 
exposed in the branchial chamber which is plainly only a 
Integu- 
mentary. 
External 
Features. 
* The following description, except in the case of the gills, will apply equally 
well for the crayfish (Astacus), the lobster (Homarus), or the shrimp (Crangon), and 
with very little modification for the crab (Carcinus). 
