162 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
generations; or tlie variations may be II. Acquired; these may be 
(a) due to external actions, mechanical, physical, chemical, or com- 
posite, Q 3 ) due to function, such as use or disuse, or (y) to pathological 
processes, or (8) correlated with the preceding variations. Lastly, varia- 
tions may be inherited (a) from parents, (/3) indirectly, by influence, 
(y) by atavism, from ancestors. 
Biological Regions and Tabulation Areas.* * * § — The principles which 
appear to have dominated Mr. C. B. Clarke in the preparation of this 
memoir appear to be chiefly these. The preparation of biological regions 
presupposes a tabulation of material on some geographical framework ; 
the use of natural biological regions to tabulate upon has been found 
inexpedient, and is absolutely impracticable as, with increasing know- 
ledge, their boundaries become ever more complex ; if naturalists would 
agree to tabulate on one geographical framework, each might have every 
liberty in making out his own regions and subregions for exhibition of 
his results ; and yet all the advantages aimed at by Mr. Wallace in 
enforcing the employment of one set of regions might be secured. The 
framework of areas and subareas which the author puts forward will be 
best understood if his maps, which we cannot reproduce, be consulted at 
the same time. 
B. INVERTEBRATA. 
Blood of Invertebrata.f — Dr. A. B. Griffiths has a general review 
of the characters of the blood in various groups of invertebrate animals, 
in which the results of other observers are incorporated, with original 
investigations ; some of these we have from time to time noted. 
Nervous Tissues of Invertebrates.^ — Dr. A. B. Griffiths has investi- 
gated the chemical constitution of the nervous tissues of various Molluscs 
and Arthropods. He finds that, as in higher animals, the constituents 
are very liable to chemical change ; in Insects and Crustacea neuro- 
keratin is replaced by neurochitin, the composition of which is C = 50, 
21; H = 7, 64; N = 4, 86. 
Report on Animal Parasites. § — Dr. M. Braun commences his report 
with an account of general works. That of Looss || should appeal to a 
wide circle of readers. L. v. Graff, inter alios , deals with the relation 
of parasites to man and domestic animals. L. G. Neumann ** has an 
extensive work on the parasites of domestic animals, which is illustrated 
by numerous figures, and has a carefully prepared bibliography. 
J. Frenzel || discusses the relation of enteric parasites to the digestion 
of living tissue. 
* Phil. Trans., 183 B (1893) pp. 371-87 (2 maps). 
f Proc. Roy. Soc. Edinb., xix. (1892) pp. 116-30. 
X Comptes Rendus, cxv. (1892) pp. 562 and 3. # 
§ Centralbl. f. Bakteriol. n. Parasitenk., xiii. (1893) pp. 59-61, and 99. 
|| 4 Sckmarotzertkum in der Thierwelt,’ Leipzig, 1893, 186 pp. 
% 4 Die auf den Menschen ubertragbaren Parasiten der Hausthiere,’ Graz, 1891, 
40 pp. 
** 4 Traite des maladies parasitaires non microbiennes des animaux domestiques,’ 
Paris, 1892, 767 pp., 364 figs. 
tt “ Die Verdaunng lebenden Gewebes und die Darmparasiten,” Arch. f. Auat. 
u. Phys. (Phys. Abth.), 1891, pp. 293-314. 
