96 I 



NOTES ON THE ANATOMY AND REPRODUCTION OF 

 PALUDESTRINA STAGNALIS. 



By CAPT. H. E. quick, M.B., F.K.C.S. 



(Read before the Society, October iS, 1919). 



The following notes on Paludestrina stagnalis make no pretence to 

 completeness, but Prof. Boycott's discovery of Parthenogenesis in 

 P. jeiikiusi {/. of Conch., xvi., 2) makes the record of the condition 

 in allied species of interest. 



The ovary occupies the upper whorls of the spire lying superlici- 

 ally between the body wall and the liver. The thin-walled oviduct 

 follows the convexity of the body whorl. Its lower portion is thicker 

 and lined by cubical ciliated cells, and runs with the rectum to open 

 within the mantle cavity close to the anus. 



The testis occupies the middle whorls of the spire. The vas is a 

 thick walled tube, lined by cubical ciliated cells, and appearing as if 

 convoluted and twisted on its own axis. 



The penis is relatively large and mobile, arising from the right 

 dorso-lateral body wall beneath the mantle margin. ^Vhen fully 

 extended it reaches beyond the base of the right tentacle. Beneath 

 the epithelial covering is a coat of longitudinal and then a coat of 

 circular muscle fibres. The areolar tissue of its interior is traversed 

 by a narrow ciliated duct, which is thrown into folds when the penis 

 contracts. The terminal fifth of the lumen is non-ciliated. The 

 mobile spermatozoa can at times be seen issuing from the terminal 

 orifice. 



In this district F. stagnalis inhabits Swansea beach near high water 

 mark, Parkmill estuary, and Oxwich salt marsh. At Parkmill the 

 shallow pools are only flooded at spring-tides, after which their muddy 

 floors are crowded with P. stagnalis. During neap tides the pools 

 dry up in summer, and the mud floors become fissured. 



On Aug. 7th, 19 19, after a fortnight's drought, numerous P. stagnalis 

 were found semi-dessicated at the roots of the short grass and thrift 

 on the edges of the dry pools. Placed in brackish water they immedi- 

 ately became active, and on Aug. i6th a clutch of twenty-five eggs in 

 a gelatinous envelope was seen on the side of the vessel. These eggs 

 hatched as free swimming veliger larvai on Sept. 9th. An individual 

 of this group proved, on dissection, to be a male, with active 

 spermatozoa. 



The eggs capsules are frequently found attached to the shells, and 

 coated with small sand grains. They are laid from May to August, 

 and very likely at other periods. 



