REVIEWS. 
157 
of keeping aquaria ; the Aleyonaiian zoophytes are still waiting for their 
historian, hut the remainder of the forms properly included under the term 
Zoophytes by Johnston and the older naturalists, have now met with worthy 
treatment at the hands of the Rev. Thomas Hincks, whose valuable treatise 
on the British Hydroid Zoophytes appeared in 1868, and is now followed by 
a splendid work on the Marine Polyzoa. The few fresh-water species are 
omitted, as having been made the subject of a special treatise by Dr. Allman, 
published by the Ray Society. 
The Polyzoa, which include among others the well-known Flustrce , or sea- 
mats, and many of the slender, branching, horny zoophytes which enter into 
the composition of the so-called sea-weed baskets and pictures familiar to 
visitors to our watering-places, were regarded by Linnaeus and his successors, 
down to the time of Lamarck and Cuvier, as very nearly related to the 
Sertularia and other Hydroid polypes, the last-named author, in the second 
edition of his Regne Animal (1829), only separating them from the latter 
(his Polypes vaginiformes ) as a distinct family under the name of ‘ Polypes 
a cellules,’ the distinction being founded on differences of the polypidom, and 
the animals in both cases said to resemble Hydra, although the greater 
simplicity of the Sertularian polype seems already to have struck Cuvier. 
But at an earlier period, it had been noticed that the differences between 
the animals of different species of so-called Sertularia were very consider- 
able. Thompson’s observations were not published until 1830, but he states 
that they were made soon after 1820. He called the newly-recognized 
form of polype a 1 Polyzoa,’ in opposition to the term ‘ Hydra ’ applied to 
the individual zooids of the true Sertularians and their allies. In the 
meantime, however, the distinction had been noticed by Grant and Milne 
Edwards ; the fact that the new type of structure could be assimilated to 
that of the Ascidians was recognized, and shortly afterwards the group was 
removed from the division of Zoophytes to that of the Mollusca, and 
placed in the immediate vicinity of the Ascidians. Of late years there has 
been considerable discussion as to the propriety of the position thus 
assigned to the Polyzoa, several eminent authorities being inclined to remove 
them to the Yermes, under which rather miscellaneous head it seems difficult 
to find their allies ; whilst others still maintain their molluscan affinities. To 
the latter opinion Mr. Hincks adheres, and he strengthens his point here by 
adducing what appears to be a strict homology between the Polyzoon and 
the embryo of the bivalve Mollusca. 
Another matter about which there has been a considerable amount of 
dispute is the name which ought to be given to this class of animals. 
Thompson’s memoir was published in December, 1830, and in June, 1831, 
•appeared the first part of Ehrenberg’s Symbolce Physicce, in which the 
Prussian natuialist established a class, ‘ Bryozoa,’ for the reception of the 
Polyzoa and of some other organisms, which he associated with them under 
a mistaken notion of their affinities. The question that has arisen is as to 
wLich of these names should be adopted. On the mere question of priority 
there need be no doubt, always assuming that Thompson proposed the forma- 
tion of a new group of zoophytes under the name of Polyzoa ; otherwise 
* Bryozoa,’ if admissible on other grounds, will be the earliest name 
applied to the class. The objection raised to 1 Polyzoa ’ is that it was used 
