THE CHROMATOPHORES OF ANIMALS. 109 



of Hermione hystrix differ, according to Jourdan (Arch. 

 Zool. Exp., v., p. 94, 1887), from the polygonal unpig- 

 mented cells of the same layer by their smaller size. Where 

 the epithelium is columnar, as in Telepsavus, the pigment is 

 contained in the outer portions of the cells (Claparede, Ann. 

 Sed., pi. xiii., figs. 9 and 19, 1873). 



Pigment may also, however, be extensively deposited 

 in the cells of the peritoneum, as in Nereis pentonealis and 

 perivisceralis (Claparede). In the former case it is violet, 

 in the latter brown in colour. " Chloragogen " cells — en- 

 larged pigmentiferous cells of the splanchnopleure — are also 

 widely distributed among Annelids. The blood in many 

 Annelids also contains special highly coloured respiratory 

 pigments. 



Much-branched pigment-cells of a yellow or reddish- 

 brown colour are found in certain otherwise transparent 

 pelagic Polychsetes, such as Pont odor a pelagica, Phalacro- 

 phorus pictus (Greeff, Zeit. f. w. Zool., xxxii., p. 237, 1879), 

 and Iopsilus phalacroides (Viguier, Arch. Zool. Exp. (2), iv., 

 1886). They appear to lie in the connective tissue, and 

 seem to have a certain relation with the nervous system. 

 In form and arrangement they foreshadow the chromato- 

 phores of Crustacea. 



In Oligochaeta the pigments are generally mesodermal. 

 Interesting exceptions to this rule are furnished by various 

 species of Aiolosoma and Ctenodrilus, in which a number of 

 ectodermal cells scattered over the body are known to con- 

 tain large oily drops, generally coloured in various brilliant 

 tints of green (Von Kennel, Arb. Zool. Inst. Wurzburg, v., 

 1882 ; Beddard, Proc. Zool. Soc, 1888). 



7. Gephyrea. Respiratory and excretory pigments are 



common. The dermal layer of the skin of Sipunculus 



nudus contains numerous pigment aggregations, apparently 



cellular, the precise nature of which cannot be said to have 



been satisfactorily ascertained (Andreae, Zeit. f. w. Zool., 



xxxvi., 1882). It is interesting to note that in the larva 



somewhat similar bodies are found within the ectoderm. 



These are stated to disappear during the metamorphosis 



of the larva (Hatschek, Wien Arbeiten, v., 1884); but the 



8 



