1891] Mechanical Origin of Structure in Pelecypods. II 
The genus Deodrilus ® proposed by Mr. Beddard has its sole 
representative in Ceylon. It seems to combine the character of 
several of Benham’s families, and its exact position is uncertain. 
Beddard regards it as nearest Typhzeus and the Geoscolicide, 
with some affinities with Pontodrilus and many Eudrilide. 
Beddard announces a forthcoming classification of the earth- 
worms. 
In the same paper he describes a connection of the nephridia 
with the terminal region of the intestine as occurring in the New 
Zealand species Acanthodrilus multiporus. These nephridia are 
connected with the general nephridial network found in the Plec- 
tonephrica. Whether the portion of the intestine with which 
they are connected is proctodeal or entodermic is unsettled. Bed- 
dard makes some interesting comparisons with the respiratory 
trees of the Gephyrea chetifera, and also with the malpighian 
tubes of the Hexapods. 
THE MECHANICAL ORIGIN OF STRUCTURE IN 
PELECY PODS. 
BY ROBERT TRACY JACKSON. 
jie is desired in this paper on Pelecypods to call attention to some 
cases recently studied in which the structure of the animal 
seems to be the direct consequence of the physiological reaction 
induced by the mechanical requirements of the environment; or ` 
to cases of “mechanical genesis,” as they have been termed.’ 
Several of our examples are cases in which similar forms are built 
up on similar lines of development, but in widely separated or 
totally distinct groups of animals. They therefore afford evidence 
10 Cn the Structure of a New Genus of Oligochzta (Deodrilus); and On the Presence ot 
Anal Nephridia in Acanthodrilus. Quart. Jour. Mic. Sci., XXXI., p. 467, 2 pls., 1890. 
1 This paper is taken largely from a recently published memoir, to which the reader is 
referred for a fuller discussion of many facts presented. See Phylogeny of the Pelecyp- 
oda, the Aviculidz and Their Allies; by Robert Tracy Jackson. Mem. Bost. Soc. Nat. 
Hist., Vol. IV., No. 8, July, 1890, pp. 277-400, pls. XXIII.-XXX. 
