hee no te 
a ils Miele bell lai 
both of which exhibit affinities. with the Crustacea 
and the Avachnida. 
The Lycnogonide or Spider Crabs are sluggish 
spiderlike marine animals with slender bodies and 
four pairs of long slender legs, into which run prolon- 
gations of the intestine ina most remarkable manner, 
Most of the species are small, but we have given 
a representation of Colossendus gigas at fig. a, which 
is a very large species, with a straw-like body more 
than half-a-yard long, which is found in the Atlantic 
Ocean at the depth of 3,000 fathems. 

45 
to be related to the extinct Trilobites. They are 
large animals with an arched shield covering the head 
and thorax, which is jointed to a nearly hexagonal 
plate covering the abdomen, which is followed by a 
long movable and pointed tail. The limbs consist 
of 6 pairs of footjaws terminating in pincers, and 
5 pairs of swimming and gill-feet. These animals 
inhabit the tropical seas, and are edible; they are 
sometimes to be seen in aquariums. Lzmulus Poly- 
phemus, represented at fig. b, is a dark green species 
| about two feet long. — The more typical Crustacea 
The Pecilopoda, or King Crabs are considered | 
may be arranged in the following series: 
Sketch of Orders of Crustacea: 
Section I, Malacostraca. 
Order I. Thoracostraca. 
Suborder I. Decapoda. 
Tribe I. Macrura. 
Tribe Il. Brachyura. 
Suborder II. Schizopoda. 
Suborder UL. Czmacea. 
Suborder IV. Stomatopoda. * 
Order II. Arthrostraca. 
Suborder I. Amphipoda. 
Suborder II. sofoda. 
It is impossible to give a general description 
which would apply to all the Crwstacea, for although 
everyone is familiar with crabs, lobsters and shrimps, 
yet there are other groups like the fish-parasites and 
barnacles, which have much more outward resem- 
blance to worms or molluscs, and only betray their 
real relationship to the Crustacea in their meta- 
morphoses. The forms which have not retrograded 
by parasitism have more than 4 pairs of legs, which 
easily distinguishes them from the other Arzzculata, 
and two pairs of antenna, exhibiting great variations 
in form. They breathe by means of gills. Only 

Section Hf. Entomostraca. 
Order I. Branchiopoda. 
Suborder I. FPhyllopoda. 
Suborder II. Cladocera. 
Suborder III]. Branchtura. 
Order II. Ostracoda. 
Order III]. Copepoda. 
Suborder I. Copepoda natantia. 
Suborder Il. Copepoda parasita. 
Order IV. Cirripedia. 
Suborder I. 
Suborder II. 
Thoracica. 
Rhizocephala. 
the Cirripedia (Barnacles) are hermaphrodite. When 
the young leave the egg, they seldom resemble the 
parents, but generally undergo a complicated meta- 
morphosis; and in some cases, they are developed 
from unfertilised eggs. The three highest Orders, 
which show their close relationship in possessing the 
same number of segments in the abdomen, are 
classed together as Malacostraca. Many species are 
valuable as human food, and others play an im- 
portant part in the system of nature as food for 
fish and other marine animals. 
Section I. Malacostraca. 
Order I. 
The upper part of the body which consists of 
13 amalgamated segments, is covered wholly or 
partially by the carapace, a large shield covering the 
head and thorax. The abdomen is composed of 
7 segments, and the compound eyes are generally 
placed on moveable stalks. The different form and 
arrangement of the limbs in the various Orders forms 
a remarkable instance of the manysided developments 
which organs identical in origin may undergo in 
the course of development. The gills are appen- 
dages of the limbs, and are generally branching. If 
we dissect a crab or a crayfish, an easy and simple 
experiment, which will give us a good idea of the 

Thoracostraca. 
anatomy of an articulated animal, we must first open 
the back (contrary to the usual process in the case of 
a vertebrate animal), when we first arrive at a long 
vessel which represents the heart; below this lies 
another vessel, the digestive apparatus, which has a 
sac-like enlargement (the stomach), which is bordered 
at the sides, and partially embedded in extensive 
glands. When we have removed all this, as well as 
the muscles, we find, sharply defined on the dark 
chitinous armour, a white thread-like organ with 
knot-like expansions which throw out slender threads 
laterally. This is the nervous system, which is not 
unlike a rope-ladder in form. In the crabs, the body 
