36 SUMMARY OF CURRENT RESEARCHES RELATING TO 



whicli the author had previously arrived, that the occurrence of chloro- 

 phyll in animals is invariably due to the presence of inclosed algse. 



The yellow cells of different animals differ from one another very 

 considerably in their structure ; but all agree in possessing a chloro- 

 phyll-like pigment, a nucleus, and a starch-like product of assimila- 

 tion. In almost all were found tvv^o different products of assimilation, 

 viz, 1st, grains containing a vacuole, and therefore appearing like a 

 ring in optical transverse section, never doubly refractive, always 

 colourless or very pale blue, and coloured by pure iodine brown 

 or violet, or, under certain circumstances, blue-violet ; 2nd, com- 

 pact granules, doubly refractive and of irregular form, of a reddish 

 or violet colour, and not changed by treatment with iodine. The 

 first of these is undoubtedly a substance allied to starch. 



When large quantities of the green cells are carefully treated with 

 filtered water, they usually assume the form of zoospores with two 

 cilia at the anterior end; their pigments being still usually in the 

 form of parietal plates, and having starch-grains in their interior. 



Morphologically the yellow cells are very different from chloro- 

 phyll-bodies, and correspond to unicellular chlorophyllaceous algae, 

 while physiologically they behave altogether like chlorophyll-grains. 



By a fresh series of experiments the author has confirmed the 

 view previously held that the hosts or " phytozoa " make use, for 

 their own nutrition, of the products of assimilation which the algae 

 obtain in excess through the influence of light. 



MoUusca. 



Skin of Cephalopoda.* — P. Girod regards the dermis of cephalo- 

 pods as being essentially formed of connective tissue, the cells of 

 which may become the centre for the formation of reticulated tissue, 

 connective bundles, pigment-cells, or the so-called iridocysts. We 

 find two strata, one formed of pigment-cells which are motile chroma- 

 tophores, the other of iridocysts. The former is the most interesting, 

 and has been very extensively studied. For its further comprehension 

 it is well to distinguish the two constituent parts of the chromato- 

 phore : the pigment-cell, which is nothing else than the central spot, 

 filled with coloured granulations, and the radial bundles which form 

 a complete crown around the cell. The chromatophore, thus con- 

 stituted, moves in a space which may be called the peripheral space. 



The pigment-cell varies in size according to the degree of con- 

 traction or expansion of the chromatophore. The basal cell of the 

 radial bundle is rounded during contraction, elongated and flattened 

 during expansion. The fibres which make up the bundle approach 

 one another during contraction, and separate on expansion. The 

 interfascicular spaces are elongated during contraction, wider and 

 flatter during expansion. Girod denies the contractile muscular 

 nature of the radial bundles, and regards them simply as formed of 

 connective tissue. It is clear, therefore, that, on this view, the 



* Arch. Zool. Exp^r. et Gen., i. (1883) pp. 225-66 (1 pi.). 



