56 REPORT — 1855. 



are in the J'oung from ten to twelve in number, M'hereas in the adult from 

 sixty to eigiity can be counted, and the cornea assumes a deeper tint ; being 

 crimson in the larva, it becomes purple or almost black in the adult. 



The young are generally of a more or less deep orange colour ; in some 

 species they are cornuous and transparent^ and in the development are 

 generally less marked than the adult. 



The large hand in Orchestia holds in the larva a nearer contrast to that 

 of the female than to the larger claw of the male ; it is therefore extremely 

 probable that this organ likewise increases in growth ; a fact also remarked 

 by Rathke*, regarding the warty development of the posterior leg of the 

 same animal which still goes on with increasing age. 



In Hyperia the larva bears so little resemblance to the parent, that it 

 has been pronounced by Edwards, who first observed the fact, and Mr. Gosse, 

 to be a metamorphosis; but since, even in the higher types, the immense 

 variety of change from the Zoe. to the adult animal is but the result of subordi- 

 nate becoming more important parts, together with development of others not 

 yet present, and therefore hardly acceptable under the signification of meta- 

 morphosis, as understood in true Insecta; we can scarcely subscribe to the 

 great alteration of form as a metamorphosis in Hyperia, which is one of degree 

 only, and of which we shall give a figure in the forthcoming 'British Edrio- 

 phthalma.' 



On the Nei'vous System. — This part of the subject has been attended to 

 with more care than perhaps any other part of the animal, by MM. Audouin 

 and Edwards, in a memoir published by them on the nervous system of 

 Crustacea generally. 



To this paper, which has been made the standard of all authors, we shall 

 now refer the reader ; and in this Report only draw attention to particular 

 details of more or less importance, which we have noticed from actual obser- 

 vation in dissections made upon Talitrus locusta, and which are given in our 

 figures of the nervous system of that Amphipod in PI. XXII. accompanying 

 this Report. 



The scheme of the arrangement is peculiarly annular, perhaps typically 

 crustacean ; a ganglion corresponds to every segment of the animal, each 

 being united to the other by two cords, which correspond, but are not 

 connected with each other. From each ganglion on the right and left, a 

 double branch is given off; the one passes to the legs, the other probably to 

 the branchial organs. In the male, the ganglion corresponding with the 

 seventh segment of the pereion (thorax), which supports the male organs, 

 appears a little larger than the others. From the cords intermediate between 

 the ganglia originates on the external side of each a corresponding nervous 

 thread, which again divides into two, and probably supplies the internal vis- 

 cera of the animal. These threads have not been recorded in the memoir 

 quoted as belonging to the Amphipoda, but analogous ones are figured in the 

 ' Histoire des Crustaces,' pi. 11. figs. 3, 4, as belonging to the Stomapoda. 

 But a more important variation in the nervous system of the Amphipoda 

 exists in the arrangement of that part which belongs to the cephalic region. 

 The first ganglion (Plate XXII. fig. 2 E) of the pereion (thorax) rests upon 

 the sternal portion of its own segment, from which anteriorly a sudden de- 

 pression takes place to the infra-cesophageal ganglion (B), which lies beneath 

 a calcareous arch (O), which earlier in this paper has been described as being 

 the dorsal aspect of the three segments, which fused together support the 

 maxillae and maxilliped. 



From the infra-cesophageal ganglion several nerves originate to supply 

 * Faunen de Crim. Phil. Trans. St. Petersburg. 



