112 MisceUaneous, 



The tip of the projection into the subjacent mesoderm, which is 

 thus formed, is constituted hy the large cell, destined to form the 

 essential portion of the ehromatophore. Sinking still further, it at 

 last finds itself at the bottom of a little ectodermic pit, and com- 

 mences to become ver}' large ; its protoplasmic contents divide into 

 two layers, a more solid one, which condenses round the nucleus, 

 and another, more limpid, in which the former is immersed. 



This cell, the wall of which has thickened concurrently with its 

 expansion, finishes by being attached to the invaginated ectodermic 

 cells by a narrow area only, and at last separates from them and 

 becomes free in the mesoderm', a few cells of which fix themselves 

 upon it and drive it deeper in. Henceforth it loses its spherical 

 shape, and nearly resembles a biconvex lens. 



But while this has been taking place in the ectoderm the meso- 

 dermic cells have not remained inactive. Beneath the ectodermic 

 invagination they arrange themselves to the number of five or six 

 in a circle ; successive radical divisions then take place, and the 

 cells are finally some twenty in number, forming a circle of greater 

 area. In shape they are of an elongate ovoid. It is at this period 

 that, suspended above this circle, the ectodermic cell becomes free, 

 and there finds itself naturally enclosed ; it increases in size, and 

 bv its circular rim comes in contact with this wreath of ovoid cells. 

 The ehromatophore is thus constituted. The protoplasm of the 

 chromatic cell assumes a yellow or rose-colour, and the peripheral 

 cells become elongated and transformed into fibres. 



The muscular or connective nature of these radial fibres has been 

 the subject of much discussion. If muscular they would, by their 

 sudden contraction, have induced the movements of the pigmented 

 matter ; if connective, they would not have had any immediate 

 action on these movements. According to my own observations, 

 both of these views are nevertheless true, though in succession. 

 The young peripheral fibres are muscular and animated by contrac- 

 tile movements which are most distinct, though they have no sort of 

 action on the pigmented protoplasm ; they simply cause the entire 

 apparatus to move in the direction of the contracted fibres. It is 

 not until later that these fibres lose their contractile quality, become 

 similar to bundles of fibres, and serve exclusively to retain the whole 

 ehromatophore in position. 



The ehromatophore, then, appears to me to be formed of an essen- 

 tial portion, the pigmented ectodermal cell, and of accessory meso- 

 dermic parts, which primitively resemble muscular fibres, and later 

 on become connective. 



As regards the nerve-endings belonging to each ehromatophore, 

 they can be rendered visible in the living animal by means of a 

 special preparation of methylene blue. We then see with the 

 greatest clearness the cutaneous nervous plexus of the chromato- 

 phores, each fibre of which terminates in a slight swelling, which is 

 applied to the chromatic cell, though it does not appear to me to 

 penetrate it. — Comptes Eendi(s, t. cxii. no. 1 (Jan. 5, 1891), 

 pp. 58-(30. 



