ALLMAN, ON POLYZOA. 39 
signify the outer and inner membranes of which the tubular 
portion of the polyzoary is composed. With respect to the 
composition of these membranes, a full description is given 
of the structure of the endocyst, which may be observed most 
favourably in Lophopus crystallinus. In this species it is com- 
posed of large, irregularly-shaped cells, filled with a colourless 
and transparent fluid. The mode of formation of these cells 
may be satisfactorily followed. 
It would seem, from some appearances noticed by Pro- 
fessor Allman, that the endocyst is pervaded by a system of 
canals of extreme delicacy, which constitute an irregular 
network in its substance; a curious and important fact, if 
confirmed by further observation. 
The ectocyst appears m every case to be absolutely struc- 
tureless, and the presence of cellulose could never be detected 
in it. The reactions of the pergamentaceous ectocysts of 
Plumatella are in favour of this tissue being composed of 
chitine. The “ ectocyst,’ therefore, it 1s observed, of the 
Polyzoa would seem to differ—at any rate, chemically—from 
the test of the Tunicata. 
In the account of the digestive system, an elaborate 
account is given of the histological structure of the alimen- 
tary canal, which is somewhat complex. <A curious peculi- 
arity appears to characterise the alimentary canal in the 
phylactoleematous Polyzoa, as distinguished from that in the 
marine gymnolemata—the absence, viz., of cilia in any part 
of its tract, except at the mouth and upper portion of the 
cesophagus. 
Ina note appended to the “Account of the Organs of Respi- 
ration and Circulation,” a full account is given of the anatomy 
of Pedicellina. This contribution to our knowledge of this 
curious and aberrant form of Polyzoa is of great mterest. 
The account given by Professor Allman of the generative 
system, reproduction, embryology, gemmation, and develop- 
ment in the Polyzoa is very complete and satisfactory. We 
have here a full description of the curious mode im which the 
different stages of the process of development of the embryo 
are carried out, and from the account given; it would appear 
that the external part of the embryonic sac becomes eventu- 
ally the ectocyst of the future adult Polyzoon. The develop- 
ment of two polypides in each embryonic sac, except in the 
case of Plumatella fruticosa, is a remarkable fact, with which 
—as, indeed, with the curious process of development alto- 
gether—we were previously unacquainted. 
VOL. VI. E 
