94 THE VOYAGE OF H.M.S. CHALLENGER. 



entire length of the animal ; the posterior pair of pereiopoda is still very short, being 

 only 4 mm. long as compared with 30 mm., the length of the first pair, which is the only 

 one not broken, and which is generally but little more than half of the second and 

 third. Up to this stage, the most advanced in the collection, the animal still retains its 

 Phyllosoma condition, without the slightest sign of any branchial structure whatever. 

 The nervous system gradually becomes more definite in character but as yet the pereionic 

 ganglia are distinct from each other both longitudinally and laterally. The cerebral mass 

 consists of three lobes, the frontal and two lateral. The former supplies the organs of 

 vision, the latter send large branches to the antennae, while one or two small branches 

 there subdivide and go to the antennal gland, which in this larger specimen appears to 

 consist of a number of thick-walled convoluted chambers or cavities. 



From the cephalic ganglia two long slender nerves go directly back to the oral appa- 

 ratus, which they pass, one on each side, and continue until they enter the pereion, where 

 they enlarge and unite to form a long wavy mass, from which small lateral branches 

 are given off apparently to join the gnathopoda and the anterior appendages which, 

 as yet, are in an immature condition. Passing from this ganglionic mass, the neural 

 cord divides and forms double ganglia, in three successive pairs, which go respectively to 

 the three anterior pairs of pereiopoda. The next supplies the fourth pair but differs 

 from all the preceding in consisting of four ganglionic masses forming a quadrangle. 



The fifth pair of pereiopoda is as yet in a very immature condition, but whether from 

 injury to the specimen in mounting or from some other cause, lean find no corresponding 

 ganglionic centre. Whether the posterior or quadrangular group of ganglia supplies it I 

 could not determine, although I am induced to believe it does, but the space between 

 this and the next ganglion was obscure. 



The next and following ganglia differ from the preceding in being spherical and in 

 having no central division ; they are close together, and each ganglion is nearly as large 

 as the somite that it supplies is long ; there are only five ganglia, and these correspond 

 to the five anterior somites of the pleon ; none were visible in the sixth joint and telson. 

 The next specimen is evidently the young of another species, and agrees closely with 

 that which Milne-Edwards has described and figured under the name of Phyllosoma 

 stylicornis, 1 but it has the cephalon narrower anteriorly and proportionally longer 

 (PI. XIIc. fig. 1). It is 30 mm. in length, and was taken off St. Thomas Island, West 

 Indies, in the month of March, whereas that of Milne-Edwards is recorded from the Indian 

 Ocean. Its most remarkable feature is, that although it is one of our largest specimens, 

 the pleon is not more than 1 mm. in length, and none of the pleopoda are present except 

 the posterior pair, and these are in a rudimentary stage. On the other hand all the 

 pereiopoda are as far advanced as those of the preceding specimens, and the posterior 

 pair is very much more so, and stands at the extremity of the posterior angle of the 



1 Hist, cles Crust, vol. ii. p. 4S3, pi. xxviii. figs. 1-7. 



