ENTOMOSTRACA. 303 
Order 3. Copepoda.—Elongated Crustaceans, usually with distinct seg- 
ments. There is no dorsal shell. There are five pairs of biramose 
thoracic appendages, but the last may be rudimentary or absent. 
The abdomen is without limbs, and of its five segments the first 
two are sometimes united. The females carry the eggs in external 
ovisacs. Most Copepods move very actively in the water, jerking 
themselves rapidly by means of their thoracic legs, or swim more 
gently by means of their second antennz. Many are ecto-parasitic, 
especially on fishes (‘‘fish-lice”), and are often very degenerate. 
The free-living Copepods form an important part of the food- 
supply of fishes. 
Cyclops, free and exceedingly prolific in fresh water. Its 
appendages are:—antennules, antennz, mandibles, first 
maxille, second maxille, four pairs of flattened biramous 
thoracic legs united across the middle with those of the 
opposite side, another rudimentary pair, and probably the 
genital valve. Cetochzlus, Calanus, free and abundant in 
the sea. In Chondracanthus, as in many other cases, the 
parasitic females carry the pigmy males attached to their 
body. Caligus, a very common genus of “‘fish-lice.’”’” In 
the carp-lice (Arvgu/us) the mouth is a sucker with sharp 
stilets and the second maxillze form adhesive discs. 
Lernea, Penella, etc. The adult females are parasitic, and 
almost worm-like. The males and the young are free. 
Order 4. Cirripedia.—Barnacles and acorn-shells, and some allied 
degenerate parasites. 
Marine Crustaceans, which in adult life are fixed head down- 
wards. The body is indistinctly segmented, and is enveloped 
in a fold of skin, usually with calcareous plates. The anterior 
antennz are involved in the attachment; the posterior pair 
are rudimentary. The oral appendages are small, and in part 
atrophied. In most there are six (or less frequently four) 
pairs of two-branched thoracic feet, which sweep food particles 
into the depressed mouth. The abdomen is rudimentary. 
There is no heart. The sexes are usually combined, but 
dimorphic unisexual forms alsos occur. The hermaphrodite 
individuals occasionally carry pigmy or ‘‘complemental” 
males. The spermatozoa are mobile, which is unusual 
among Crustacea. 
Lepas, the ship-barnacle, is as an adult attached to floating logs and 
ship-bottoms. The anterior end by which the animal fixes itself is 
drawn out into a long flexible stalk, containing a cement gland, the 
ovaries, etc., and involving in its formation the first pair of antennee and: 
the front lobe of the head. The second antennz are lost in larval life. 
The mouth region bears a pair of small mandibles and two pairs of 
small maxillz,—the last pair united into a lower lip. The thorax has 
six pairs of two-branched appendages, and from the end of the rudi- 
mentary abdomen a long penis projects. At the base of this lies the 
anus. Around the body there is a fold of skin, and from this arise five 
calcareous’ plates, an unpaired dorsal carina, two scuta right and left 
