ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 517 



be found, and the sponge must then have extended its growth into the 

 deserted channels with such rapidity as to fill every minute branch 

 before the oyster could bar it out by the secretion of enough new 

 shell to stop apertures tdW inch diameter. 



But this is not all. The burrows occupied by Cliona branch in 

 all directions and diminish in diameter as they extend inward, which 

 would represent a method of boring quite inconsistent with the habits 

 of any known borer. Again, in these specimens, the sponge was 

 found in small spots on the thin lamina?, around the sides and anterior 

 edges of the shell which represent its most recent external growth, 

 and in such cases the lamina? were perforated from side to side. 



Protozoa. 



De Lanessan's Protozoa.* — This will be found a welcome book 

 by microscopists, as it is copiously illustrated with woodcuts and 

 deals with the subject in a very readable form, while yet being far 

 beyond a merely popular handbook. 



The author's leading divisions are Monerans, Amcebans, Forami- 

 nifera, Eadiolaria, Infusoria (flagellate, ciliate, and tentaculate), and 

 he claims to have originated a new plan for such a book differing from 

 that of ordinary treatises. He commences in each case with con- 

 sidering in its adult state an individual species chosen as the best 

 type of the group (by its being readily procured, best known, &c), 

 dealing with all the details of its organization, with its physiological 

 functions, its habits, and the development of its organs, considerable 

 importance being given to embryology. He then describes the other 

 leading forms of the group, and when all these have been disposed of 

 a separate chapter sums up the common characters of the group, 

 its relations with neighbouring groups, and its classificatory divisions. 



The author considers that a great mistake is made when the 

 converse course is adopted and the characters of the group are dealt 

 with, noticing the peculiarities of the organization of the different 

 types of the group in the course of the general description. By this 

 method, he says, " a Mollusc becomes a kind of abstract entity 

 clothed with characters rendered so vague by the generalization that 

 the student has the greatest difficulty in discovering them in the 

 specimen given him to dissect." 



Taking the Amcebans for an example the following is the author's 

 arrangement : — 



1. The principal forms. 



(a) Gymno- Amcebans. Under this head are described A. princeps, 

 A . coli, Podophrys elegans, Pelomyxa palustris, Dactylosphozrium radio- 

 sum, D. polypodium, D. vitreum, Hyalodiscus rubicundus, Petalopus 

 diffluens, Plakopus ruber, Podostoma filigerum, and Mastigamoeba aspera 

 (9 figs.). 



(b) Theco- Amcebans. — Pseudochlamys patella, Cochliopodium pel- 

 lucidum, Difflugia oblonga, Quadrula symmetrica, Arcella vulgaris, and 

 Amphizonella violacea (6 figs.). 



* J. L. De Lanessan, ' Traite de Zoologie. Protozoaires,' vii. and 336 pp. 

 (281 figs.) 8vo, Paris, 1882. 



