182 Mr. H. J. Carter on the Colouring Matter of the Red Sea. 



well defined as is the thorax by the number of segments which 

 compose it, we may certainly take the three divisions of the body, 

 as they are constituted in insects, as the standard to which the 

 segments of the higher Crustacea are to be referred, if we desire 

 to settle what are their cephalic, thoracic, and abdominal seg- 

 ments. We will not state, then, that the thorax of Arthropoda 

 is normally composed of seven segments. In Isopoda and Am- 

 phipoda, where the part usually called the thorax is divided into 

 seven leg-bearing segments, the segment corresponding to the 

 prothorax of insects has completely disappeared, its legs being 

 added to the head in the shape of a lower lip with palpi ; the 

 first and second of the seven leg-bearing segments are analogous 

 to the meso- and metathorax, and the five others, as well as the 

 segments of the so-called abdomen, to abdominal segments, — 

 the abdomen being here, as in all higher Crustacea, composed 

 of a greater number of segments than in insects, and divided 

 into an anterior (pectoral) and posterior (caudal) portion*. To 

 the five segments constituting the pectoral part of the abdomen 

 in Isopoda the five leg-bearing segments of Decapoda are ana- 

 logous, whose thoracic segments are all united to the head (their 

 legs constituting the three pair of accessory masticatory organs) 

 and whose pectoral portion also enters into the part usually 

 called the cephalothoraxf. 



EXPLANATION OF PLATE VI. 



Fig. I. Locusta viridissima, <? , seen sideways. 



Fig. ii. The same, $ ; apex of abdomen. 



Fig. in. a. Pachytylus migratorius, c? , seen from beneath. 



Fig. in. b. Terminal segments of the male of Pachytylus migratorius, seen 

 sideways. 



Fig. iv. a. Pachytylus migratorius, °. ; last abdominal segments, seen side- 

 ways. 



Fig. iv. b. The same, seen from beneath. 



Fig. v. Forficula gigantea, S ; abdomen seen sideways. 



Fig. vi. Forficula gigantea ; metathorax (m) and first two abdominal seg- 

 ments. 



XX . — Note on the Colouring Matter of the Red Sea. 

 By H. J. Carter, F.R.S. &c. 



To those who have sought for all that has been published on 

 the colouring matter of the Red Sea, it will be well known that 

 the excellent memoirs on this subject by M. C. Montagne in 

 1844, and M. C. Dareste in 1855 (both in the 'Ann. des Sc 

 Nat./ the former in ser. 3 (Bot.) t. ii. p. 331, and the latter in 



* Erichson, Entomographien, pp. 14-16. 



f Brandt, Medic. Zoolog. ii. p. 58; Erichson, I. c. p. 19. 



