ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
803 
Mr. Bidder suggests that, primitively, the afferent pores of Sponges 
are perforated excretory cells derived from the endoderm, while the 
ectoderm is a layer of cells excreting constantly from the intercellular 
jelly, their glass-shaped form having been developed to expose the 
greatest possible surface to the medium from which the excreted sub- 
stance is derived. They have been differentiated on the exterior as a 
covering to the nutritive and reproductive cells of the Sponge, in order, 
by reason of their noxious contents, to form some protection to the naked 
protoplasm. 
It is suggested, as a proper subject for expert chemical analysis, the 
investigation of the extent of the alliance of the substance excreted by 
Calcarea in the granules of the Metschnikoff and ectoderm cells with 
the so-called spongin. The last term, as used by zoologists, is applied 
to a number of different nitrogenous substances found as supporting 
structure in a large group of more or less allied Sponges. The author 
suggests, as a working hypothesis, that the yellow granules of Ascetta 
clathrus are a soluble nitrogenous excretion which is highly mutable, 
and readily gives rise to the less soluble substances which occur with 
it in the granules of other Homocoela. The horny sponges are, it is 
suggested, those that have learned to retain within their bodies this 
nitrogenous secretion of the protoplasm, common to all Sponges, till it 
has formed one or other of those more or less insoluble products which 
are grouped together under the term Spongin. 
Recent Researches on Sponges.* — Dr. 0. Maas emphasizes the 
diploblastic nature of the sponge-embryo ; the layers might be spoken 
of as ectomesoderm and endoderm. From his own studies on the 
development of Esperia , Topsent’s observations on Clionidae, and 
Mincliin’s account of Leucosolenia clatlirus , the author regards the 
contractile elements as originally ectodermic. A primitive state with 
ectodermic contractile cells persists in Leucosolenia , but it is not justi- 
fiable on that account to include all contractile cells as ectodermic (as 
Topsent does), for in the more highly differentiated forms the contrac- 
tile elements form part of the middle stratum, as F. E. Schulze has 
described in horny sponges. There is as much reason for calling the 
spicule-forming cells and the amoeboid wandering cells ectoderm. 
Histology of Calcareous Sponges. f — Dr. R. v. Lendenfeld calls 
attention to some points in Mr. E. A. Minchin’s paper on Leucosolenia, J 
in which he thinks an incorrect account has been given of his views, or 
structures regarded in an erroneous manner. 
Protozoa. 
Merotomy of Ciliated Infusorians. § — Prof. E. G. Balbiani gives an 
account of some fresh experiments on the division of Ciliated Infusorians. 
The more or less large fragments which are separated from the body of 
a Stentor generally close quite easily the wound produced by the 
section ; the edges of the wound come together almost at once, owing 
to the elasticity of the cuticle, and the contractility of the muscular 
* Biol. Centraibl., xii. (1892) pp. 566-72. 
f Zool. Anzeig., xv. (1892) pp. 277-9. % See this Journal, ante , p. 491. 
§ Ann. dc Microgr., iv. (1892) pp. 369-407,449-89 (3 pis.). 
