ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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seems to be useless as a basis of classification for the whole group, 
although it is so used by Pelseneer. The author suggests the possibility 
of the ascending limb of the gill-filament being a new structure which 
has suddenly developed in the forms most closely connected with the 
Lamellibranchs that have plate-gills. 
Elimination of Foreign Bodies in Lamellibranchs.* — M. H. Coupin 
gives an account of some observations with Pholas dactylus, which show 
that the palps serve chiefly to prevent large foreign bodies from reaching 
the mouth and so the digestive tube, the walls of which are very delicate. 
Driven by the palps to the orifice of the ventral siphon, the foreign 
bodies, such as Pholas meets with when making its holes, are driven 
outwards. 
Molluscoida. 
a. Tunicata. 
Salpa in Relation to the Evolution of Life.f — As may be supposed 
from its title, Prof. W. K. Brooks’ essay has a wide bearing, of the kind 
which it is exceedingly difficult to summarize. Salpa is regarded as 
being only remotely descended from a pelagic, Appendicularia-\ike 
ancestor, and is more immediately derived from a sessile form, similar 
in its habit of life, and, essentially, in structure also to the Ascidians. 
To understand the position and significance of Salpa in the economy 
of Nature it is necessary to know at least the broad outlines of the con- 
ditions under which oceanic life has been evolved. The author com- 
mences, therefore, with contrasting terrestrial and marine life; the 
fauna of mid ocean is next described, and then the primary food- 
supply. . 
In discussing the origin of pelagic animals, Prof. Brooks points out 
the probability of there having been, long after the crust of the earth 
had acquired essentially its present character, a supply of oxygen so 
scanty that it was used by pelagic organisms in the surface water ; so 
that life on the bottom was impossible at a time when the superficial 
water supported a luxuriant fauna and flora. During this period the 
proper conditions for the production of large and complicated organisms 
did not exist, and while the total volume of life was very great, it con- 
sisted of the organisms of minute size and simple structure which the 
author terms the primitive pelagic fauna and flora. 
The origin of the Crustacea, and the phylogeny of the Metazoa, are 
next passed in review, after which there is a section on “ the discovery 
of the bottom and its effect on evolution ” ; the primitive bottom-fauna 
must have had the following characteristics : — 
(1) It was entirely animal, and at first depended directly upon the 
pelagic food-supply. 
(2) It was established around elevated areas in water deep enough 
to be beyond the influence of the shore. 
(3) The great groups of Metazoa were rapidly established from 
pelagic ancestors. 
(4) There was a rapid increase in the size of the bottom animals and 
hard parts were quickly acquired. 
* Comptes Rendus, cxvii. (1893) pp. 373-6. 
f Studies from Biol. Laboratory, John Hopkins Univ., v. (1893) pp. 129-211. 
1893. * 3 E 
