On the Anntomy 0/ Palmlcstriuii jcnkinsi. 425 



LVII. — On the Anaioiny.of Palu lestrina jonkiiisi. 

 By G. (;. KOBSON, B.A. 

 (Tiiblished by pennissiou of the Trustees of the British Museum.) 



[Plate XV.] 



Thk Ga3tro|)ocl Pahiclestnna jenkinsl, first described by 

 E. A. ISmith (13) in 1869, lias been lor the last thirty years 

 an object of intinest for British malacologists on account of 

 its rapid spread throutcii the inl.and waterways of England, 

 Wales, and Ireland. It has rec^-ntly attracted fresh attention 

 owing to the discovery made by Boycott (2), and conlirnied 

 by Quick (10) and Gatenby and liobson (MS.), that it is 

 parthenogenetic. Tiie 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 niiile has been discovered. 



Tiie 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 encountered in the preparation of 

 material for study owing to the animal's contractility, small 

 size, and power of resistance to antesthetics. It was hence 

 practically impossible to get satisfactory expansion of the 

 anterior part of the body. Small shreds of tobacco and 

 alcohol gave the most satisfactory results for this jnirpose ; 

 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 eliminaling narcotization, and, 

 after very carefully cracking away the shell, placing the 

 animals directly in Bouin's solution (picru-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 °/q alcohol and proceeded with as usual. 



External Features and Behaviour. 



The shell and external features have been describe^l bv 

 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 IManarian, 

 waving its long alentler tentacles and moving the lieail from 

 side to side in an inrjuisitive manner. As Smith points out, 



Ann. ct Mat/. X. lUsl. Scr. '.». \'vl. v. 2'J 



