30 
Guide to Crustacea . 
Table-case important part in the economy of nature than any other 
No. 2. Crustacea. 
Many Copepoda live as parasites on fishes, and other aquatic 
animals, and as a result of this parasitic life their structure 
becomes greatly modified and degenerate. 
The Order Eucopedoda (Eig. 11) includes the great majority 
of the Copepoda, both free-living and parasitic. True paired com- 
pound eyes are never present, but the median unpaired eye is 
often well-developed. Most of the free-swimming species are 
extremely minute, few attaining the size of Euchaeta norvegica, of 
which specimens are exhibited. The enlarged drawings show the 
brilliant colours of some pelagic species. 
Fig. 11 . 
Caloccilanus pavo, one of the free-swimming Copepoda of the “ plankton.” 
Enlarged. (From Lankester’s “ Treatise on Zoology,” after Giesbrecht.) 
The parasitic species are usually much larger than those 
which live a free life, and a number of species taken from common 
fishes are exhibited. Pennella, which is found on whales and 
fishes, is the giant of the sub-class, some specimens being even 
larger than that exhibited here. 
The order Branchiura includes a small number of fish- 
parasites whose exact relations tor the other Copepods are obscure. 
They possess a pair of compound eyes, and a piercing stylet, con- 
nected with a poison-gland, in front of the mouth. Argulus 
foliaceus is common on fresh- writer fishes in this country. The 
large Argulus scutiformis is taken from marine fishes in Japan. 
