NOTES AND MEMORANDA. 
223 
advocate a belief in the so-called ‘ germ theory of disease/ or rely 
upon the exclusive doctrine of a ‘contagium vivum/ seem to be 
absolutely broken down and refuted. We may give that attention to 
the appearance and development of independent organisms in associa- 
tion with morbid processes which the importance of their presence 
demands, but we must regard them as concomitant products, and not 
at all, or except to any extremely limited extent, as causes of those 
local and general diseases with which they are inseparably linked.” 
Hydroida of the Gulf Stream. — Dr. Allman’s Report on the 
Pourtales Collection of Hydroids from the Gulf Stream describes a 
very large number of new and interesting forms, and is one of the 
most important contributions to their natural history that has ap- 
peared of late years. It is illustrated by thirty-four plates. 
A Water-lens Microscope. — Mr. G. M. Hopkins, in the ‘ Scientific 
American,’ describes a microscope which, it is claimed, “ renders a 
drop of water available as a microscope lens by confining it in a cell, 
thus obviating the tremor of the early water microscopes, a defect 
which rendered them almost if not quite worthless.” The cell con- 
sists of a brass tube f inch long and ^ to inch internal diameter, 
blackened, with a thin piece of glass cemented to the lower end, and 
having in one side a screw for displacing the water, to render the lens 
more or less convex. Several bushings may be fitted to the upper end 
of the cell to reduce the diameter of the drop, and thus increase the 
magnifying power of the lens. 
The Structure and Development of Sponges. — In Siebold and 
Kolliker’s ‘ Zeitschrift f. wiss. Zoologie,’ vol. xxx. part 4, is an article 
“ On the Structure of Deniera semitubulosa : a Contribution to the Ana- 
tomy of the Siliceous Sponges,” by Dr. E. Keller. Mr. E. Ray Lan- 
kester, in a ‘ Biological Note ’ contributed by him to ‘ Nature ’ of 
July 18, gives the following summary of the article, with additional 
observations of his own — 
The sponges are at present attracting a very large amount of atten- 
tion from zoologists and are undergoing investigation in the fresh 
condition, so that their living soft tissues are subjected to the refined 
methods of modern histology. Professor Franz Eilhard Schulze, of 
Gratz, is foremost in this study, the way in which was led by Ernst 
Haeckel in his monograph of the Calcispongiae. Dr. Keller, of 
Zurich, who has previously published on the development of certain 
calcareous sponges, has now given attention to Beniera semitubulosa, 
O. Schm., a representative of the commoner marine fibrous sponges. 
Schulze, by the use of silver nitrate, discovered a differentiated epithe- 
lial covering to the body surface, which was previously denied by 
Keller, who now admits Schulze’s observation to be correct, and adds 
a similar observation of his own on Reniera. Keller describes the 
syncytium of Reniera, denies the existence of muscular cells, and 
recognizes certain “ nutritive wander-cells ” in the body-wall of the 
sponge. His observations on “ starch-containing cells ” are of special 
importance. He was led to attach a high functional importance to the 
nutritive wander-cells which pass inwards from the flagellate endo- 
