﻿On the Occurrence of a Stcpposed Australasian Hydroid. 81 



The ocean currents are not inconsistent with that view. 

 While a specimen from South Australia would tend to drift 

 towards New Zealand, a specimen set free upon the west 

 coast of Australia (and the minutiae of the present specimens 

 agree with those of West Australian specimens) might be 

 borne by an Indian Ocean south equatorial current round 

 Cape Colony, whence, caught up by a north- travelling branch 

 of the Antarctic drift, it might be carried into an Atlantic 

 south equatorial current moving north-westwards into the 

 Gulf of Mexico, and thence the Gulf Stream drift might 

 bear it to the waters of the North Sea. 



The journey is a long one — it has probably left its traces 

 in the empty perisarc and the polyzoon-encrusted twig — and 

 the chances against its successful completion are many, but 

 it seems the only satisfactory way of accounting for the 

 interesting occurrence of so distinct a Hydroid species off 

 the Scottish coast. 



The suggestion has been made that the specimen may 

 have been taken accidentally, along with packing or ballast, 

 on board some ship loading at an Australasian port, and was 

 afterwards set free on the discharge of the ballast in the 

 neighbourhood of Aberdeen. Such a mode of transport, how- 

 ever, involves so many coincidences of place that it seems 

 highly improbable ; and, besides, the condition of the specimen 

 itself argues against the supposition, for it is difficult to 

 believe that a number of large and fragile colonies could be 

 first cast upon a rough sandy or shingly shore (suitable 

 for ballast), and afterwards tossed about amongst ballast at 

 loading and unloading, without suffering a considerable 

 amount of damage. And yet in the present case, as the 

 accompanying photographic reproduction (Plate III.) very 

 clearly shows, almost all the colonies are complete, with 

 naturally terminated stems and perfect pinnse, upon prac- 

 tically every one of which, in the more mature colonies, are 

 perched exceedingly delicate, loosely attached gonangia. 

 The perfection of structures so fragile excludes the possi- 

 bility of carriage by methods other than the most gentle, 

 but is such as we might expect in a water-borne specimen, 

 the sport of gently flowing oceanic currents. 



VOL. XVll. G 



