PHYLLOPODA. 
287 
In tiie family Apodidce, containing the genera Apus and Lepidurus, the anterior 
end of the body is covered with a carapace, projecting from the head over the free 
segments of the thorax. The hinder border of this 
carapace is deeply cut out, and near its front end there is 
a pair of contiguous compound eyes. The mouth is 
bounded in front by a large upper lip and belli 11 d by a 
deeply cleft metastoma, or lower lip. Both pairs of 
antennae are short. The jaws consist of a pair of 
mandibles and two pairs of maxillae; these are followed 
by eleven pairs of thoracic limbs, and there are append¬ 
ages on the abdomen, sometimes numbering as many as 
fifty-two pairs. The last segment of the abdomen bears 
a pair of long filaments, and sometimes, as in Lepidurus, 
a distinct caudal plate. These crustaceans occur in the 
fresh waters of most countries. They swim on their 
backs, using the legs as paddles; and the eggs are capable 
of surviving long periods of drought when embedded in 
dried mud. I11 the second family—the Branchipodidae 
—the body is also elongate, but there are no appendages 
to the abdomen, which consists of nine segments, while 
there are eleven pairs of thoracic appendages. The head- 
shield is not developed backwards, and the large separated 
eyes are supported upon distinct stalks. In the male, the 
second antennae are converted into claspers. These forms 
likewise swim upside down. Some (. Branchipus ) occur in a> MALE 0P Branchipus grvbel 
fresh waters, but others (Artemia) prefer briny pools and (nat. size) ; b, female of 
flourish in water so strongly charged with salt as to be f “7 
fatal to other crustaceans. Artemia salina (enlarged). 
Class Prototracheata. 
This term is applied to the group now claiming attention, because in many 
respects it occupies a place between the Tracheates and Worms, and is consequently 
regarded as allied to the ancestral form from which all Tracheates have been 
evolved. Unlike the true Arthropods, the limbs are not jointed; and the tough 
integument is covered with bristle - bearing papillae, but is not divisible into 
segments. The long body is shaped like that of a caterpillar or slug, and to the 
sides of its lower surface are attached a number of short more or less conical legs, 
each tipped with a pair of strong claws. The head is supplied with a pair of stout 
longish antennae, at the base of each of which, on the outer side, is an eye. On 
the lower surface of the head is placed the mouth, supplied with fleshy lips and 
two pairs of toothed horny jaws ; and on each side of the head there is a modified 
appendage known as the oral papilla. The chief features to note in the internal 
organisation are the presence of segmentally arranged kidneys— one opening at the 
base of each leg—and the wide separation of the two strands of the ventral nerve- 
chord. This last character is found in some of the lower worms, and the numbers 
