ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
667 
deep-sea animals keep tlieir balance, and the author finds that equilibra- 
tion is not interfered with when he covers the eyes of crayfish, Narcoris 
cymicoides, Corixa carinata, Acilius sulcatus , Ilybius uliginosus , JEschna 
juncea, Agrion elegans, Pieris brassicse, and a Phryganid. The crayfish 
moves as usual, but knocks his head against the side of the aquarium ; 
the insects flew well, but went high up in the air. 
The simplest means of orientation is that afforded by a difference 
between the specific gravity of the organism and that of the medium, 
for thus the animal is made aware of up and down directions. This can 
be shown by the behaviour of aquatic animals when placed in a medium 
specifically heavier than they are if they are specifically heavier than the 
water, or specifically lighter in the reverse case. In such conditions 
those which normally breathe in water swim upside down ; those which 
breathe air keep their normal position and come to the surface. The 
author discusses the mechanical conditions which explain these facts. 
Correlations of the Volumes and Surfaces of Organisms.* — 
Dr. J. A. Ryder finds that there are only three ways in which living 
Nature has found it possible to escape the conditions imposed by the 
simple aggregating impulses of the forces of gravitation and surface 
tension. All three have been resorted to, with all their multiform con- 
sequences, by the Protozoa and Protophyta, so that it is now difficult to 
decide which of the three was the most primitive form — the segmenting 
spherical, the alternate cylindrical, or the flattened discoidal. 
The vacuolation and gradual dilatation of the simple spherical form 
into a vesicle or segmented blastula probably led to the evolution of the 
Metazoa, while indefinite lengthening and branching of cell-aggregates 
seems to have been the line along which plant-cells became coherent, 
and gave rise to the Metaphyta. 
The changes of shape suffered by all organisms may be reduced to 
two categories : — 
I. Indefinite stretching in linear directions, of which dichotomy is 
only a special form. 
II. Indefinite flattening, compression, or attenuation of some or all 
of their substance into a flat plate or into laminae. 
B. INVERTEBRATA. 
Catalogue of Parasites. j — Messrs. C. W. Stiles and A. Hassall have 
prepared a preliminary catalogue of the parasites contained in the 
collections of the U.S. Bureau of Animal Industry, U.S. Army Medical 
Museum, the Leidy collection, and in the collections made by the authors 
themselves. The host, the locality, the collector and collection are stated 
in a regular manner. 
Food of two Commensals. :£ — M. H. Coupin has studied the habits 
of Nereilepas fucata, the worm which is very commonly found living 
with Pagurids in the shells of Buccinum ; it is generally supposed that 
the annelid lives on the dejecta of the crustacean ; but the author’s 
* Contrib. Zool. Lab. Univ. Pennsylvania, i. (1893) pp. 3-36 (1 pi.). 
t Veterinary Mag., 1894, pp. 245-53, 331-54. 
X Comptes Kendus, cxix. (1894) pp. 540-3. 
