108 SCIENCE PROGRESS. 



orange or red, and consists either of coloured fluid within 

 the vacuole alone, or of granules found in the peripheral 

 protoplasmic portion of the cell and subsequently dehisced 

 into the fluid contents of the enlarging central vacuole. 

 The mesodermal pigment is in the form of black or brown 

 granules deposited in the peripheral portions of the cells. 

 The two kinds of pigment — bright ectodermal and dark 

 mesodermal — may exist separately or together, and the 

 general colour of the Planarian depends upon the prepon- 

 derance of one or other of the different elements. 



4. Nemertea. The brilliant colours of these animals 

 are said by M'Intosh and Hubrecht to be due to pigmented 

 cells of the connective tissue. Burger, however, has shown 

 {Zeit. f. wiss. Z00L, 1., 1890) that in the most primitive 

 Nemertines, e.g., Carinel/a, the pigment resides, not in 

 elements of the connective tissue, but in the non-o-landular 

 elements of the ectoderm. In all higher forms the pigment 

 is contained in branched pigment-cells of the ordinary type, 

 which are situated either entirely beneath the basement 

 membrane of the ectodermal epithelium, as in Metanemer- 

 tines, or partly above and partly below this membrane, as in 

 Eupolia. In the latter case the pigment-cells are associated 

 with the enlarged gland-cells of the ectoderm — a fact which 

 suggests their derivation from the same embryonic layer. 



5. Hirudinea. The pigment is entirely mesodermal, 

 and is extensively deposited in cells of the connective and 

 vasifactive tissues. The pigment found in the spaces 

 between the mallet-shaped cells of the epidermis has in- 

 truded from the connective tissues (Lankester and A. G. 

 Bourne). 



6. Annelida. The bright orange colour of the Archi- 

 annelid Dinophilus tceniatus is due to pigment contained 

 in large branched connective tissue cells. Orange-coloured 

 granules are also contained in the cells of the nephridia 

 (Harmer, /Wr., M. B. A., i., 1889). 



According to Claparede (Annelides Chetopodes dn Golfe 

 de Naples, p. 158) the colours of Polychsete Annelids are 

 generally due to pigment distributed in the chitinogenous, 

 that is ectodermal, layer. The pigmented ectodermal cells 



