ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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survived —60°, wero mostly killed at —80° to *-90°, and were wholly 
destroyed at —150° to —160°. 
Bacteria, spores, diatoms, seeds and the like seem to defy the lowest 
temperatures. Even exposure to about — 200° in liquefied air did not kill 
either germs or seeds. Vaccine fluid, however, was rendered innocuous. 
The simpler the organism is, the greater its power of resistance. 
Each grade of structure has its limit of temperature, rising as we ascend 
the series. Thus mammals and flowering plants are relatively very 
sensitive. Sudden cooling of the higher animals is followed by an 
energetic reaction which may be found to have therapeutic importance. 
At — 100° chemical processes cease ; much more so in seeds, germs, 
and spores subjected to — 200°. Yet these seeds, germs, and spores 
revive ! Life is a phenomenon analogous to gravitation : it does not die 
as long as the structure in which it manifests itself is intact ; it is one 
of the constant forces of nature. 
Phenomena of Convergence.* — Dr. F. Werner describes convergence 
as the independent occurrence of similar organs, colourings, markings, 
movements, protective and aggressive adaptations, and the like, in types 
which are phylogenetically distinct, but which agree in having similar 
functions, habits, surroundings, &c. In short, the term convergence is 
applied to cases where similar adaptations occur in unrelated forms ; 
or convergence is, in Prof. Ray Lankester’s terminology, a case of 
“ homoplasy,” but not of “ homogeny.” 
But the distinction, easy enough in theory, is not quite so easy in 
practice. Thus, there are three snakes, Coluber oxyceplialus, C. frenatus , 
and C. prasinus , sometimes united under the title Gonyosoma , and closely 
alike in adaptation to arboreal life. Do they illustrate the divergence 
from one ancestral Gonyosoma type, or the convergence of three distinct 
species of Coluber ? In regard to forms of relatively close affinity, the 
question is difficult ; in regard to kangaroo and jerboa it is easy. 
Werner goes on to discuss (1) “ horns,” from those of a beetle to those 
of a rhinoceros ; (2) the extension of the skin to form webs, parachutes, 
and the like ; (3) the adaptations to arboreal life seen among snakes ; 
(4) adaptations to aquatic life ; (5) the characters of burrowing animals, 
e.g. reduction of appendages, tail, and eyes, obliteration of the distinc- 
tion between upper and under surface, and increase of the rostral 
region ; and scores of other examples of convergence. 
Mollusca. 
y. Gastropoda. 
Doridiidae-t — Dr. R. Bergh states the characteristics of this group 
as follows. The body is covered by two separate shields. The anterior 
shield, hardly separable in front from the small head, has slightly pro- 
jecting lateral margins, and the hind margin may overlap the posterior 
shield. The posterior shield has its hinder part prolonged laterally in 
two flat wing-like processes. The strongly developed foot is continued 
laterally into two large pleuropodia, curved upwards to cover the sides of 
the body and part of the back. The shell is sometimes of considerable 
* Biol. Centralbl., xiii. (1893) pp. 471-6, 571-6. 
t MT. Zool. Stat. Neapel, xi. (1893) pp. 107-35. 
