We have caught lately a great many small animals, of which the following is the description; they swim about from one floating substance to another and are eaten by the little crabs which are numerous in these seas.

Length of body 0.18 inch. 
Length of anterior part of body 0.1 inch. 
Length of posterior part of body 0.08 inch. 
Length of tail 0.08 inch. 
Breadth across back 0.05 inch. 
Depth from back to bottom of breast 0.06 inch.

Head and eyes, deep brilliant prussian blue; body brilliant prussian blue with a bluish green stripe on each side; tail white.  Seen through a microscope these animals appear to be a beautiful dark burnished blue mottled with silver.  The head is remarkably round and regular.

The body is divided into two portions.  The anterior portion is made up of six rings or shields, which lap over one another, and it is furnished with three legs on each side which terminate in a hooked claw; the posterior part is covered by three shields, and there was only one leg on each side.  I could not make out any tentaculae or antennae.

I was much struck by a curious circumstance today.  As we caught a great many gelatinous animals I thought this a good opportunity of taking their temperature, which, after an observation so carefully made that no error could occur, was found to be 66 degrees 5 Fahrenheit, the temperature of the air at the same time being 74 degrees.  The temperature of the water was now taken and was found to be 2 degrees 5 minutes more than that of the animals; thus giving these animals a temperature lower than that of the fluid in which they were immersed.  I conceived that some error must have been made in the temperature of the water, it was therefore taken again and found to be 69 degrees as before; this appeared to me so remarkable that I drew up a table of all the experiments which had been made on this subject, the result of which is that the mean temperature of these kinds of animals appears to be 64 degrees 9 minutes Fahrenheit; and that the greatest variation in excess is 1 degree 7 minutes; and in defect 2 degrees 9 minutes Fahrenheit.  Is it possible, then, that an animal can live in a fluid, the temperature of which is constantly varying, and preserve nearly a mean heat?

In the following tables I have entered every experiment but one which was made on the 17th of June, and in which I believe the animals to have been kept too long out of water.

(Experiments to determine the temperature of gelatinous animals which inhabit the sea: 

Experiments to determine the temperature of shellfish inhabiting the open ocean:)

This last experiment was made from a sickly specimen which had been kept for some time in the water:  the temperature of water above given is for that in which this animal was kept.

We caught again today many animals of the same family (Glaucus) as those of which a description is given in the journal for the 17th of June.