8 Dr. Gr. C. Wallicli on Physalia and 



preciable diminution in size as compared with the original 

 sporangial frustule ; and in this theory every requisite for the 

 completion of the genetic cycle of the species would appear to 

 be supplied. 



II. — On Physalia and certain Scombroid (?) Fish which are 

 frequently associated with it in Tropical and Subtropical 

 'Seas. By G. C. Wallich, M.D., F.L.S. 



Mr. Collingwood's interesting paper on " Oceanic forms of 

 Hydrozoa," which appeared in the ' Annals ' for November 

 1867, brought to my recollection some additional facts in con- 

 nexion with Physalia which came under my observation 

 during repeated voyages to and from India, and of which I 

 retain copious notes. To these facts I will advert immediately ; 

 but I would point out, en passant, that the stinging-properties of 

 this Hydrozoon are by no means so novel as Mr. Collingwood 

 seems to think, every sailor with whom I have come in con- 

 tact who has once traversed tropical and subtropical latitudes 

 having been well aware that the " Portuguese man-of-war " is 

 not a creature to be handled with impunity. The stinging-pro- 

 perty resides in the tentacles, not in the polypites, and is pro- 

 duced by the discharge of acontia from minute oval sacs which 

 are distributed at regular intervals along these organs. 



Although I have invariably failed in my efforts to preserve 

 the pneumatophore of Physalia in anything approaching to 

 its pristine condition, I have been able readily to secure the 

 tentacles in such a manner as to have retained their character 

 up to the present period, namely, over a space of eleven 

 years. This has been effected simply by placing the pneuma- 

 tophore on a card or board (to which it adheres at once 

 through a certain tenacity peculiar to it) and by then winding 

 off the tentacle in the same way that one may wind off a skein 

 of silk or cotton. The extensile quality of the organ is such 

 that I have sometimes succeeded in stretching it, from its 

 natural length of from 3 to 6 inches, to some 8 or 10 yards, 

 and this without once breaking the continuity of the thread. 

 On being so extended, the tentacle forms an extremely deli- 

 cate flattened band, composed of several parallel fibres of 

 highly contractile tissue arranged longitudinally, each fibre 

 being from k6 \ to 1 7 ' of an inch in diameter*. On this, 

 or, rather, imbedded in this composite filament, the acontia- 

 sacs are distributed. 



* A specimen of a piece of the preserved tentacle, mounted on an ordi- 

 nary slide in Canada balsam, without further preparation, is to be seen in 

 the cabinet presented by me to the Royal Microscopical Society. 



