236 J. S. HUXLEY. 



PLATE I. 



FIGS. 1-4. s-day plutei in HgCL, n/i, 000,000. 



FIG. i. After 24 hours. 



FIG. i a. The most frequent type, with arms considerably resorbed, aboral 

 end dilated. Anal view. 



FIG. ib. Similar, but arms more resorbed. The red pigment grains are 

 here represented. Anal view. 



FIG. ic. Similar, but not quite so much arm-resorption ; marked dilatation 

 of the trunk-region. The epithelium of the trunk and aboral regions is 

 exceptionally thin. Lateral view. 



FIG. id. More complete dedifferentiation. The trunk and aboral regions 

 are contracted instead of dilated ; consequently the aboral ends of the spicules 

 are not separated, and the trunk epithelium is thicker than normal. Anal 

 view. 



FIG. IB. Similar, but with more pronounced arm-resorption. Anterior 

 view. 



FIG 2. After 72 hours. 



FIG. za. Specimen with arms vestigial and dense, thin form, and clumping 

 of mesenchyme. The stomach is normal, the intestine and oesophagus shrunken. 

 Lateral view. 



FIG. zb. Aboral end of the same, under higher magnification. The light 

 masses are composed of pale yellow cells with few granules. The dark 

 bodies are red pigment. Quite aborally is a mass of slightly different clear 

 cells. 



FIG. 2c. The commonest type. The anal arms are totally absent, the 

 oral arms and lobe almost entirely so. The skeleton of the oral arms is 

 just protruding. The trunk and stomach are swollen, but the intestine con- 

 tracted. Oblique anal view. 



FiG. zd. No trace of arms or of the form-differentiation of the oral end 

 remains. On one side, the skeleton of the oral and anal arms has disap- 

 peared. The gut is shrunken, and its parts lie nearly in a straight line. 

 Oblique anal view. 



FIG. 2e. Complete dedifferentiation of the form of both oral and trunk- 

 regions. Body opaque and dense, filled with clumped mesenchyme. Skeleton 

 reduced to two straight rods. Lateral view. 



FIG. 3. After 96 hours. 



FIG. 3d. Protrusion of skeleton, disintegration of oral arms only. Trunk 

 region still somewhat expanded. Lateral view. 



FIG. 3&. Specimen dedifferentiated in all regions, with incipient death- 

 changes. A mass of red pigment aborally. Disintegration of whole oral 

 region beginning. Anterior view. 



FIG. 4. A pair of plutei found grown together after 72 hours. Lateral 

 view. 



FIG. 5. A 4-day pluteus in HgCL w/2,ooo,ooo, after 120 hours. Note the 

 remains of the ciliated band, the reduced stomach but dilated oesophagus, and 

 the abnormal skeleton. Lateral view. 



