Mr. C. Collingwood on Oceanic Forms of Hydrozoa. 313 



elegant, brown, turquoise-studded species, similar to one I bad 

 already obtained in Victoria Harbour, Labuan, and of which, it 

 may be here mentioned, I found a small crab within the um- 

 brella, beneath which it appeared to reside. 



To show the vast numbers of these animals which swim freely 

 in the ocean, I will mention that, in the Atlantic, in lat. 3^° S. 

 and long. 17° W., we encountered a shoal of these animals, all 

 of the same species, the individuals of which were among the 

 most beautiful in form and colouring that I have ever met with. 

 Just before sunset we passed through them for a space of two 

 hours, during which time we had traversed ten miles. Sup- 

 posing that this shoal were at least as broad as long, it was easy 

 to calculate roughly that there could not be less than thirty 

 millions of individuals constituting it, an estimate probably far 

 below the truth. I procured one, and made a careful drawing 

 of it while still living. 



The only exception I met with to the rule I have mentioned 

 (namely, that when Hydrozoa floated they appeared in consider- 

 able shoals of one species only) occurred in the great calms 

 which I encountered in the North Atlantic Ocean, in the first 

 fortnight of July, and which extended more or less over upwards 

 of a thousand miles, during which, on two or three occasions, I 

 saw several species of Hydrozoa mingled with vast numbers of 

 compound Ascidians. Some of them were new and strange 

 forms, such as I have nowhere seen figured, some abundant, 

 others but fev/ in number, only appearing occasionally, and 

 therefore very difficult to capture from a moving ship. One of 

 these I did succeed in taking ; but there were at least three or 

 four species besides the Physalice and Velellce. 



It occasionally happened that the observation of a shoal of 

 Hydrozoa pointed out some curious facts from which interesting 

 deductions might be made. Thus, while passing through the 

 Indian Ocean, in lat. 13° N., during an entire day (March 17), 

 we ran through shoals of Aurelia, meeting from time to time 

 patches in which they were too numerous to be counted, and in 

 each of which there were many hundreds. A noticeable fact I 

 remarked with regard to them, viz. that, without any exception 

 that I could discover, these Awelice were, during the whole day, 

 swimming in the same direction, or with the wind. We were 

 steaming nearly due east, and a breeze was blowing a little 

 south of east ; and the umbrellas were all inclined one way, and 

 pointing in the direction towards which the wind was blowing. 



On another occasion, in a dead calm, on a beautiful day, off 

 the river Min, I observed great numbers of a large white species. 

 The edges of the umbrella were frilled, and nuujerous long and 

 delicate threads stretched out straight and parallel; but what 



