EPETRA. 237 
long coiled malpighian tubules opening into the cloaca. In 
addition to possessing two kinds of excretory 
organs, the spider also has two kinds of respira- 
tory organs. The two pulmonary sacs are situated in the 
antero-ventral part of the abdomen and consist 
of large chambers -containing a number of flat 
horizontal /amelle with thin walls. Stigmata put their 
cavities in communication with the exterior. There are in 
addition four trachez opening, as stated, by a ventral 
aperture in front of the spinnerets. They do not differ 
essentially from the trachez of the insects. Hence the 
spider has two sets of breathing organs, pulmonary sacs 
and trachez. 
The ovaries are paired tubes uniting to form ovéducts 
which open into a median uéerus. The uterus opens into 
the genital pouch, into which also open 
two seminal receptacles. The pouch is 
provided with a kind of gonapophysis, called the epzgy- 
nium. The ¢estes are sitnple tubes with vasa deferentia 
uniting into a spferm-sac with a median aperture just behind 
the stigmata. 
The eggs are laid in holes and corners during the autumn, 
and are often enveloped in silky cocoons. ‘They have a 
: large amount of yolk, and the development 
is embryonic. They hatch in the spring, 
the young spider differing but little from its parent. The 
spiders form the order Avaneina of the class Arachnida. 
(For General Characters of Sub-Phylum Arthropoda, 
see page 240). 
Excretory. 
Respiratory. 
Reproductive. 
Development. 
PHYLUM ANNULATA. 
The Axnulata form one of the three great phyla of the 
Metazoa. They are typically elongated plano-symmetric 
animals. They always have three primary layers, the meso- 
derm filling more or less of the space between the ectoderm 
and endoderm. The whole body is segmented or made up 
of a number of segments or metameres, in which many 
organs are repeated. In the lower types there can be dis- 
tinguished a pre-oral part, in front of the mouth, called the 
prostomium, and a segment immediately behind the mouth 
