no SCIENCE PROGRESS. 



question arises as to whether they may not have some con- 

 nection with the dermal deposits of the adult. Balls of 

 pigmented cells also occur in the sub-epidermal tissues of 

 Echiurids (Spengel, Zeit. f. w. Zoo/., xxxiv., 1880). 



8. Crustacea. Pigments may be deposited either in the 

 ectodermal epithelium or in special highly branched sub- 

 epithelial cells, usually referred to the connective tissue and 

 known as chromatophores. The latter are chiefly found in 

 Malacostraca, but are also known to occur among Ostracoda 

 in various species of Loxoconcha (G. W. Muller, 1884). 

 Crustacean chromatophores are usually highly mobile, and 

 in Isopods, at any rate, the chromatophore is contractile as 

 a whole (Matzdorff, Jena Zeit., 1883). The presence of 

 chromatophores is usually associated with transparency of 

 the body, e.g., Amphipoda, Schizopoda, Prawns ; epithelial 

 pigmentation naturally entails opacity, as in the larger 

 Macrura and most Brachyura. 



9. Tracheata. In Peripatus the characteristic colours 

 of the body are due to pigment granules deposited in the 

 protoplasm of the outer ends of the ectodermal cells (Bal- 

 four, Q.J. M. S., 1883). 



The same is true of Insects in general (Poulton, Proc. 

 Roy. Soc, xxxviii., 18S5 ; Trans. Ent. Soc, pi. x., 1S87) ; 

 and probably also of Arachnids. But the branched pigment- 

 cells in the central eyes of Scorpions (and Limulus) and in 

 the compound eyes of Insects are believed by Lankester 

 and Bourne to be intrusive connective tissue cells (Q. J. 

 M. S., xxiii., 1883). 



10. Mollusca. The integument is brilliantly coloured 

 in certain Amphineura, e.g., Dondersia banyulensis, but the 

 exact localisation of the pigment is not described (Pruvot, 

 Arch. Zooi. Exp. (2), ix., 1891). 



In Gastropoda the pigment occurs either in the ecto- 

 dermal epithelium, as in Haliotis, Neritina, Heteropoda, 

 Eoris ; or in the sub-epithelial connective tissue (Boll, 

 Arch. f. mikr. Anat., v., SuppL, p. 51, 1869). In the 

 latter case the pigment may reside in true chromatophores, 

 as in Pteropods and Cephalopods, or in great glandular 

 cells lying in the connective tissue but communicating with 



