PLATE XXXVII. 



Fig. 1. Ctenolabius from inner surface. Os 3^% 15 minutes, Mark. 3 days. 2 hours after 32-cell 



(8) stage. 



In the wreath are about twenty-seven cells. Protoplasm radiate around some, no nuclei in 

 division. Cap = two to four cells deep; smaller in central, larger in periphery. Round cells 

 are seen in the central portion. 



en 1, S,3 = delimited. 



en 4 not delimited against pellicle. 



en = syncytial endoderm-cells. 



Endoderm colored red, cap brown. 



For distinction, nuclei of en are red, nuclei of cap brown (Indian red). 



Most of en lie under, not outside, the margin of the cap. In a number of cases the nuclei 

 are half under cap, half exposed, [pb = periblast]. 

 Fig. 2. Two houi's after 32-cell [stage]. 42 sections .005 mm. thick, [pb = periblast]. 



(S8) The first section cuts edge of cap. Dividing line between marginal cells does not cut quite 



through the periblast. 



The twenty-first section through middle. Marginal cells small, but well colored red, while 

 the central cells are all brown. 



The twenty-fourth section shows an inner cell that is reddish, but less so than tlie marginal 

 cell. 



The twenty-seventh section shows no marginal cell. 



The thirtieth section shows red cell above the marginal cell. 



These facts are to be explained by supposing that the marginal cells are constant]}' dividing, 

 and adding cells to the cap, which soon after division become like the other cells of the cap, 

 taking brown color from osmic acid. 



At this stage the subgerminal plate is pretty complete everywhere. 



It is the upper portions of the margmal cells that are constantly cut off and added to the 

 cap, until at length the basal portion ceases to have any connection, and its nuclei spread in 

 all directions. 

 Fig. 3. Ctenolabrus. Two hours after 32-cell stage, [pb = periblast]. A portion of cap from 



(9) above. The endodermal wreath is here very distinct and contrasts with the ectoderm every- 

 where in the staining. There are ten pairs of cells and an older one, en '. Three of the pairs 

 [en^, en-, e«'°] are tangential and the rest are oblique or radially placed. In en 1 the division 

 is so nearly completed that only the most faint traces of interzonal filaments are discernible. 

 The right hand cell of the pair is in plane above the left, and [is] more sharply defined but 

 colored the same. 



en 2 shows last end of division with filaments still visible. A light line between cells indi- 

 cates plane of division which is not completed. Both cells continuous with pellicle {ph). 



en 3, [The number does not appear on the plates, but the cells are evidently those between 

 en 2 and en J,]. Division completed, inner cell highest, and best defined, but colored lighter 

 than rest of ectoderm. 



en 4, inner cell also highest but below the highest of pair en 3. Division completed and 

 outline clear in both. 



en 5, same as in 4. 



en 6, both in same plane — faint trace.s of spindle. 



en 7, division completed. 



en 8, faint spindle-cells not sharply outlined except against the fioor-cells of cap. 



en 9, outlined inner cell lighter than ectoderm and appears to be paired with the outer longer 

 cell. 



en 10, division not completed, pretty well defined but flowing into pellicle. 



All the inner cells of the pairs, except in en 3, lie in the floor of the cap, and in most cases 

 abut against surrounding cells. The paired nature of these cells is most evident. Most of 

 the imier cells are covered by ectoderm but wherever they are uncovered, they are colored like 

 endoderm. 



