Royal Physical Society. 433 



Medusa aurita, one of the large jelly-fish of the Firth of Forth. Dr 

 Wright stated that he had discovered very distinct evidence of a chitinous 

 corallum covering the attached portion of Hydra tuba, which was readily 

 seen on the specimen placed on the table. 



Dr Wright was also enabled, by the kindness of Mr Alder of New- 

 castle, to place before the Society several rare zoophytes, amongst which 

 was the Myrothela artica of Sars. He remarked that the animal was not 

 naked, as described by Gosse, but had a distinct horny corallum ; nor 

 were its tentacles wart-shaped ; they resembled the tentacles of Coryne, 

 except in having sting-cells of smaller size. He stated that, according 

 to Mr Cocks of Falmouth, the young of Myrothela was furnished with 

 long processes or legs, on which it moved from place to place as its erra- 

 tic fancy led it. But after some time it forsook its wandering life, cast 

 off its legs, developed tentacles, fixed itself to a stone, and devoted itself 

 to the more staid occupations of providing itself with food, producing a 

 family of young ones, and stinging those of its marine neighbours who 

 came into collision with it. 



III. Report of an Expedition undertaken to Explore a Route by Rivers 

 Waini, Barama, and Cuyuni, and the Gold- Fields of Caratal, and 

 thence to the River Orinoco, South America. By W. R. Holmes, 

 Esq., and W. H. Campbell, LL.D. Communicated by Professor 

 Balfour. (See " Edin. New Phil. Journal, Vol. VIII., No. I., July 

 1858.") 



IV. On the Spiral Threads of the Helix aspersa. By John Cleland, M.D. 



The exceedingly complex sexual system of the hermaphro- 

 dite gasteropoda has in various of its details furnished the 

 theme of much discussion to comparative anatomists. In 

 Helix aspersa, in addition to the other remarkable structures 

 of this system, is one whose occurrence is variable in different 

 species, and of whose functions little has been determined. I 

 allude to the long tubule which courses along the side of the 

 uterus, and opens into the duct of the seminal vesicle just be- 

 fore it falls into the vagina. 



Siebold notes that this tubule " is very long, with Bulimus 

 radiatus, Helix aroustorum, lactea, and vermiculata ; very 

 short, on the other hand, with Helix pomatia, nemoralis, and 

 candidissima ; that it is entirely wanting with Helix frati- 

 cum, strigella, and rhodo stoma.* 



* Burnet's Translation of SiebolcTs Anatomy of the Invertebrata, § 227, 

 note 13. 



