ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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external to the zooecia, as might be inferred from some of the older 
descriptions of this structure. Its cavity is morphologically identical 
with tbe body-cavity of the zooecia, and the ovicell results from the 
breaking down of numerous septa, which at first separate from one 
another a set of tubes formed at the growing edge of the colony. The 
development of the ovicell and that of the embryo normally commence 
at almost the beginning of the life of the colony. The numerous young 
larvae found in the ovicell are descendants of the single primary embryo, 
which is normally produced in one of the two zooecia first budded oft* 
from the primary zooecium. It is thought that the process cannot be 
interpreted as a form of alternation of generations. A large number, if 
not the great majority, of the secondary embryos are formed by the 
direct fission of pre-existing embryos, and are not budded off from a 
compact mass of cells as in Crisia. Further research must decide 
whether the resemblances between the development of the Cyclostoma 
and the Phylactolaema are nothing more than mere analogies. 
Revision of Jurassic Bryozoa.* — Dr. J. W. Gregory points out that 
the diagnosis of species of Cyclostomatous Bryozoa is a difficult and 
unsatisfactory task. While the Cheilostoma offer nine useful characters, 
only the least trustworthy of these are available in typical Cyclostoma, 
and at first sight it seems almost impossible to diagnose species, as even 
the genera appear to vary to a hopeless extent. While some authors 
have founded numerous species on insignificant and individual variations, 
others have thought that the sub-class affords an illustration of the theory 
of the persistence of type, and have therefore abandoned the effort to 
separate species of different ages. They have so lumped together the 
forms of different geological horizons that, if their example be followed, 
the study of the group becomes valueless. Dr. Gregory has attempted 
to find a mean between these extremes, and concludes that it is possible 
by examining a good .series of specimens to see fairly constant differences. 
For example, if we take a Jurassic specimen in which the zoarium 
contains, say two hundred zooecia, and compare it with one of a closely 
allied recent species with as many zooecia, it is not improbable that one 
zooecium in each may be found to be identical. But this does not seem 
sufficient reason for ignoring the constant differences between the 
majority of the zooecia in each. To draw up a diagnosis which will 
accurately describe each zooecium in a colony, and shall at the same 
time be sufficiently definite to characterise the species, is impossible. 
However, if we take the normal adult zooecia and compare equivalent 
ones in different species, there seems sufficient reason for supporting the 
practical validity of species in this group. The author gives a revision 
l of the genus Stomatopora , in which he recognises five species. In 
discussing the relations of these species he proposes the use of a formula 
by means of which they can be easily compared with forms of other 
ages. The result of his comparative formula is to show a gradual 
increase in the degree of development of the distinguishing characters. 
Nephridium of Phylactolsematous Polyzoa.f — Mr. A. Oka gives a 
general and critical account of these organs. He comes to the conclusion 
