7656 Crustacea, 



forms the branchial organs are developed upon the anterior portion 

 of the animal (the pereion), which supports the true or walking legs. 

 In the Isopoda they are formed beneath the pleon or posterior portion 

 of the animal, where they are arranged in the form of a succession 

 of leaflets, in corresponding pairs. It is a very curious circumstance, 

 and one that must widely separate the order in which it exists from 

 others. I have observed, in the early conditions, a strong pulsatory 

 beat at the extremity of the tail of the larva of the prawn. 



In the Squilla there are developed branches and complicated 

 branchiae attached to the pleopoda, but they differ much in form from 

 those of the Isopoda ; but, wherever situated, they have but a simple 

 oflBce to fulfil, the admission of oxygen through their thin walls to mix 

 with the blood within. 



We have often used the term blood, but Professor Agassiz has 

 shown that the fluid that passes through the veins of animals lower 

 than fish is not blood, that it wants a churning more in the vat of 

 Nature to make it into true blood ; and that the lower in the scale of 

 animal existence it-is found, the nearer in its nature is it to chyle, or the 

 first character that the substance assumes after it hiis passed from that 

 of digested food. Hence we can understand how it is that certain 

 Crustacea change their colour, in accordance with that of the weed 

 on which they live, being green where the Ulvae grow, and anon they 

 are purple where the red weeds are most abundant. 



This circumstance offers in itself a means of protection from their 

 numerous enemies, for, coloured like the weed, they creep about 

 among the branches unobserved, and hide securely beneath the sha- 

 dow of the leaves. In this way crawls about the long Idotea, whereas 

 others hide beneath the stones, or build for themselves a secure 

 abode. 



The genus Amphiihoe takes shelter in deep crevices between stones 

 or at the roots of weed, there making use of stray bits of weed and small 

 stones, which it cements by the aid of a fine thread-like substance 

 (how secreted we cannot tell), twisted and twined in every possible 

 direction. Binding the materials into a mass shapes it to a nest, 

 beneath which it takes rest in peace. I have seen them, when freshly 

 captured and put into a vase of water, take up a position upon a leaf 

 of weed and curl it to a nest, cement the edges well together, leaving 

 the ends open, and live securely there. But some are more ingenious 

 still. The variegated Podocerus, that is plentifully to be found 

 amongst the weed that attaches itself to large buoys, builds perfect 

 nests in the branches of the zoophytes that are planted there. A 



