ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 809 



increasing quantity of gelatinous substance is formed between. Into 

 this process a diverticulum of the oscular endodermal lamella pene- 

 trates, more and more completely filling it. At the end of the pro- 

 cess, where ectoderm and endoderm meet and fuse, a small rupture 

 occurs — the osculum. Except in the absence of efferent canals, the 

 young sponge is now like the adult. Further stages were not 

 observed. 



III. Theoretical. — It is not possible, without too much historical 

 matter, to review Dr. Heider's theoretical notes on sponge develop- 

 ment and history. He discusses the metazoan character, the primitive 

 form, the homology of the layers, the homophyly of the group, &c. 

 Eeferring to promorphological (relation of axes), morphological (e. g. 

 fixing by blastopore), histological and physiological differences, he 

 advocates the complete separation of the Porifera from the Coelen- 

 terata. 



Relationship of Sponges.* — In a report on the embryology of 

 Spongilla fluviatilis, Prof. A. Gotte discusses the general relations of the 

 group, and lays special emphasis on a developmental peculiarity which 

 would prevent their being closely connected with the Coelenterates. 



In the development of Spongilla, a somewhat unequal total seg- 

 mentation is succeeded by the formation of a " sterrogastrula " in 

 which the original ectoderm has grown round the endoderm. At this 

 stage the larva leaves the mother sponge. When it , has fastened 

 itself, however, to some foreign substance, a remarkable phenomenon 

 is observed, the original ectoderm ruptures and disappears as the 

 larva grows, and a new epidermis is furnished at the expense of the 

 endoderm, which thus forms the whole sponge. He denies the 

 division of the endoderm into special layers. 



It has been noted, on the other hand, in relation to Gotte's 

 observation, that in some other animals, e. g. Nemerteans (Lineus), 

 there is a similar loss of the original larval envelope, though it has 

 not been demonstrated that the ectoderm disappears in toto. 



Sponge-gemmules-t — M. A. Wierzejski has studied the nature of 

 the gemmules in the fresh-water European sponges, and gives a fuller 

 account of their histology and development than has yet been avail- 

 able. Apart from his description of their structure, and of the 

 details of their development, his conclusions are as follows : — 



The central kernel of the gemmules in all the sponges studied, is 

 formed of a group of ordinary cells in the mother sponge. The 

 elements forming the tegumentary coverings are analogous, and 

 the mode of formation is in principle the same in all the species. 

 The spicules and amphidiscs are formed outside the first envelope of 

 the gemmule. The peculiar integument in Trochospongilla erinaeeus 

 Vejd. and in Spongilla Lordii Bow., are, in their origin, analogous to 

 the slightly developed veil which is found between the amphidiscs in 



* A. Gotte, ' Abhd. z. Entwickelung d. Tiere. Heft III. Entwickelung d. 

 Spongilla fluviatilis.' Hamburg aud Leipzig, 1886. Cf. Naturforscher, xix. 

 (1886) p. 290. 



t Arch. Slav, de Biol., i. (1886) pp. 26-47 (1 pi.). 



