On the Anatomy of Paludestrina jenkinsi. 425 
LVII.—On the Anatomy of Paludestrina jenkinsi. 
By G. C. Rosson, B.A. 
(Published by permission of the Trustees of the British Museum.) 
[Plate XV.] 
THE Gastropod Paludestrina jenkinsi, first described by 
K. A. Smith (13) in 1889, has been for the last thirty years 
an object of interest for British malacologists on account of 
its rapid spread through the inland waterways of Kngland, 
Wales, and Ireland. It has recently attracted fresh attention 
owing to the discovery made by Boycott (2), and confirmed 
by Quick (10) and Gatenby and Robson (MS8.), that it is 
parthenogenetic. The precise nature of this parthenogenesis, 
whether absolute or periodic, has yet to be determined ; but 
since the animal has been under close observation no trace 
of a male has been discovered. 
The following account of part of the anatomy of this mollusc 
is based upon material obligingly presented to the British 
Museum by numerous collectors. It is hoped to publish in 
the present year an account of the reproduction of this form. 
Great difficulty was eneountered in the preparation of 
material for study owing to the animal’s contractility, small 
size, and power of resistance to anesthetics. It was hence 
practically impossible to get satisfactory expansion of thie 
anterior part of the body. Small shreds of tobacco and 
alcohol gave the most satisfactory results for this purpose ; 
but it usually happened that after slow and careful narcoti- 
zation extending over four or five days the animals would 
suddenly contract, or, when at last properly expanded and 
insensitive to touch, they were found to be dead and already 
showing signs of maceration. The best results for general 
purposes were obtained by eliminating narcotization, and, 
after very carefully cracking away the shell, placing the 
animals directly in Bouin’s solution (picro-formalin with 
a small quantity of glacial acetic acid), in which they 
were left for not less than ten hours, after which they were 
washed in 70 °/, alcohol and proceeded with as usual. 
EXTERNAL FEATURES AND BEHAVIOUR. 
The shell and external features have been described by 
Smith (13) and others; but the following additions and 
corrections may be made. 
The animal when in captivity crawls about fairly actively 
with a continuous movement of the foot like a Planarian, 
waving its long slender tentacles and moving the head from 
side to side in an inquisitive manner. As Smith points out, 
Ann. & Mag. N. Hist. Ser. 9. Vol. v. 29 
