144 ZOOLOGY. 
The Polyzoa are divided primarily into the Hntoprocta, 
(Loxosoma and Pedicellina) in which the vent is situated 
within the circle of tentacles, and the Hctoprocta, in which 
the vent lies outside of the lophophore—a group comprising 
all the higher Polyzoa (Gymnolemata and Phylactolemata). 
The development of the Polyzoa is not very complicated. 
In the marine forms, as studied by Barrois, the germ passes 
through a morula stage ; after which the cells are arranged 
into two halves, separated by a crown of cilia; at this stage 
it is called a dlastula. Atthe time of birth the ciliated germ 
is a disk-shaped gastrula, with two opposite faces or ends, 
separated by the crown, one (aboral) bearing in its centre 
the mouth-opening. This ciliated free-swimming top-like 
gastrula stage is called a trochosphere. 
After swimming about as ciliated larve (trochospheres), 
the shell or ectocyst develops, and the larva becoming station- 
ary, the cystid forms, its calcareous shell develops, and finally 
the polypide is indicated, and the primitive cell is gradually 
formed. 
As seen in Phalangella flabellans, the larva, after becoming 
fixed to some object, consists of a white pyriform mass, 
closely enveloped by an ectocyst, with numerous fat globules 
between the latter and the white mass. The ectocyst swells 
into a discoidal sac, with endocyst, ectocyst, and an external 
zone, while the internal whitish mass transforms into the 
polypide. The discoidal sac formed by the endocyst consti- 
tutes simply the basal disk of the primitive cell. The future 
opening of the cell appears on the upper surface of the cell. 
The budding out of the secondary cells of the polyzoarium 
or corm then takes place. It begins by the appearance of a 
cell placed in front and below the priraitive cell, and which 
borders it on each side ; its secondary cell then divides into 
two, each of which successively gives origin to three cells, 
and we thus arrive at an Jdmonea stage; and finally the 
Phalangella stage is reached, the process being a dichoto- 
mous mode of budding quite analogous to that which pro- 
duces the broad, flattened corm of Escharina. 
The ‘evelopment of Membranipora pilosa, which is very 
abundai t on our shores, growing on sea-weeds, is of singu- 
