334 NATURAL SCIENCE. November. 



countries, it is greatly to be hoped that Dr, Manson's theory will soon 

 be further tested. For if it be proved that mosquitoes are essential 

 to one stage of the life history of the parasite, sanitary engineers will 

 know one method by which its ravages may be checked. 



Jurassic Bryozoa. 

 Catalogue of the Fossil Bryozoa in the British Museum (Natural History). 

 The Jurassic Bryozoa. By J. W. Gregory. Pp. 239, pis. xi. Printed by order 

 of the Trustees. London, 1896. Price los. 



In the catalogue before us the diagnosis is given of seventy-seven 

 species of Cyclostomata, and of two Chilostomata. We are quite 

 accustomed to authors prefacing descriptions of Cyclostomata by a note 

 of despair as to the difficulty of classification : Dr. Gregory shows 

 how many groups of invertebrates live in tubular shells, and admits that 

 there are no diagnostic* characters by which we can positively say 

 whether a given fossil be bryozoan or not. The difficulty of this 

 decision is greatest with the Paleozoic Bryozoa, but even Bryozoa 

 from the Jurassic formation have been placed among corals, while 

 Hydrozoa such as Acanthopora, Neuropora, and Chrysoaw have now had 

 to be removed. 



Zoarial characters are considered to be the only ones available for 

 systematic work on the Cyclostomata, and Gregory accepts the 

 divisions based upon them, but shows how one genus passes into 

 another, and asks the question as to whether there are any genera in 

 Cyclostomata ; answering that there are only certain convenient, but 

 artificial, groups of species. The groups called " genera," Gregory 

 would, in the Cyclostomata, prefer to call " circuli." Another way of 

 putting our difficulty would be to say that, although there must be 

 groups of species having relationships, which in other orders we should 

 call generic, yet here, on account of the simplicity of the calcareous 

 structure and few characters available, we are often unable to 

 trace the relationship. 



The extremest pessimist may, however, hope for some increase of 

 knowledge; for example, the ovicell, which was not formerly noticed, 

 is now always keenly looked for, though the number of species on 

 which it has not yet been found is very large. Out of the seventy-five 

 species of Cyclostomata diagnosed by Gregory, he only mentions the 

 ovicells in twelve cases. No doubt by the discovery of further speci- 

 mens, and by making sections, this number will be somewhat increased. 



Useful as the ovicells are specifically, caution is required ; for a 

 character may in some cases have generic value, in others specific, or 

 the same character may have no importance, and, until a large 

 number are known, it is unsafe to make generalisations. We see the 

 danger in Gregory's attempt to use the position of the ovicell as a 

 family character in the Chilostomata, for in his " British Palaeogene 

 Bryozoa," and in the present catalogue, he makes both the Membrani- 

 poridae and the Microporidae have "external ooecia," which in neither 

 case is universal. In the subfamily Membraniporinae it is certainly 

 usual, though the best known of the Membraniporidae, M. pilosa, has 

 recently been removed to Electra ; and Norman, describing the genus, 

 writes " no ooecia known in recent species," and says that he thinks a 

 fossil described by Waters as M. Lacroixii, var. grandis, from New 

 Zealand, must, on account of its possessing an external ovicell, be 

 removed to another genus. This is apparently going too far, as the 

 writer has a specimen of M. Lacroixii from Naples with a small raised 

 ovicell, and it seems that in Savigny's plate the ovicell is figured, 

 though the artist has drawn it incorrectly, placing it below the zooecium. 



