THK DEVELOPMENT OF LKPIDOSl l^'EN I'Ah'AOOXA. 423 



pliores deep down in the substance of the l)ody are also 

 conti'acted. 



In (2) the chromatophores have their pseudopodia fully 

 extruded. In the case of pigment cells within the epidermis 

 the pseudopodia pass between the cells up towards the 

 surface. The chromatophore tends to push its pseudopodia 

 towards the light ; their movements are positively helio- 

 tropic. In the case of chromatophores lying in the super- 

 ficial layer of the dermis the cells flatten themselves out 

 against the lower surface of the epidermis, forming with their 

 pseudopodia a practically continuous light-proof coat. 



In (8) the chromatophores are seen to have their pseudo- 

 podia at the maximum of extension. 



The " Stomgd.tium.-" 



In the young Lepi do siren up to Stage 30 there is no 

 stomodasum present ; the enteric rudiment, solid in this 

 region and shai^ply marked off from surrounding tissues by 

 its cells being packed with large yolk granules, extends right 

 up to the external epiblast. 



About the stage mentioned a change is seen to be setting 

 in in the anterior part of the enteric rudiment, corresponding 

 to what will become the buccal cavity. The superficial layer 

 of the still solid rudiment is seen to be approximating in 

 character to the ectoderm. Its yolk granules become finely 

 broken up, showing that active metabolism is taking place ; 

 protoplasm and nuclei are becoming more abundant. In this 

 way there arises a layer of definite epithelium continuous 

 anteriorly with the external epiblast, sharply marked ofi^ 

 from the embryonic connective tissue outside it, but in- 

 ternally passing without any sharp boundary into the yolk- 

 laden mass inside (cf. PI. 25, fig. 6 a). It is, as it were, as if 

 an influence were spreading inwards from the external epi- 

 blast, gradually transforming the original "endoderm'^ yolk- 

 laden cells into ectoderm like itself. I find no evidence of 



