ZOOLOGY AND BOTANY, MICROSCOPY, E'J'C. 765 



special descriptive part of Ilaeckel's work is much more valuable than 

 the geueral, though too many genera have been proposed, and that there 

 was no need to make a special order for the remarkable deep-sea genera 

 Stephalia, Auralia, and Rhodalia. 



Porifera. 



Monograph of Horny Sponges.* — Dr. K. v. Lendenfeld has pub- 

 lished a monograph of the Horny Sponges ; there are 1641 (not always 

 correct) bibliographical references. In investigaKug sponges it is re- 

 commended that for the study of the canal system longitudinal sections 

 perpendicular to the surface should be made, as tboy give a much clearer 

 insight into the structure than any others ; some of the sections should 

 be as much as • 3 mm. thick, as particularly thin sections are generally 

 useless for the purpose of studying the canal system. It is important to 

 prepare portions of the skin, and the skeleton should always be studied 

 both dry and wet. Skeletons macerated in the sea and thrown up on 

 the beach are, as a rule, superior for the purpose of studying the rough 

 anatomy of the skeleton to those artificially prepared. In the general 

 accounts of the genera the author ordinarily gives a historical intro- 

 duction, and accounts of shape and size, colour, surface, rigidity, canal- 

 system, skeleton, histology and physiology, affinities of the genus, 

 statistics of the sj)ecies, key to the spec'es and varieties, and distribution. 



The author does not consider that the Horny Sj)ongesform a natural 

 order, but that ditferent groups of them are structurally allied more 

 closely to other groups of not horny sponges than to each other. An 

 artificial group, of new extent, that of the Monoceratina, is formed for 

 the Aulenidee, Spougidas, and Spongelida3, each of which represents a 

 natural group allied to a family of siliceous Cornacuspongia3. 



In the synthetical j)ortion of his work the author discusses the mor- 

 phology, histology, and physiology of Sponges, their embryology, and 

 the homology of the embryonic layers ; he also enters into the question 

 of the phylogeuy of the Sponges in general, discusses their systematic 

 position, and gives a system of Sponges. 



The jjlates give photographic illustrations of the general aj)pearance 

 of various Horny Sponges, and figures of preparations of chiefly the 

 skeleton and the canal-systems. 



Metamorphosis of Larva of Spongilla.f — Herr 0. Maas has inves- 

 tigated the development of Spongilla. He describes the young larvse as 

 swimming about by the active movement of their flagella, and as seeking 

 the darker parts of the aquarium in which they were being studied. In 

 form they are distinctly ovate; the ectoderm consists of high cylindrical 

 cells with elongated nuclei ; the interior of the larva is too dense to 

 allow of much being made out. The larvae become fixed at the anterior 

 pole, and their contour becomes much changed owing to the enlargement 

 of the surface ; at the same time the whole ectoderm becomes flattened, 

 and in time the boundaries between the cells disappear. This flattening 

 of the ectoderm results in great changes in the form of the cilia, which, 

 at first closely packed, become in time widely separated. After this a 

 peculiar change occurs in the ectoderm ; its sharp wavy boundaries 

 appear to be broken at various points ; this is due to the ectoderm at 



* London, for tlie Royal Society, 4to, 036 pp., 50 pis., 1889. 

 t Znol. Anzuig., xii. (1889) pp. 488-7. 



