112 MALCOLM LAURIE. 



greater part of the protoplasm with the nucleus collects at the 

 base of the egg. The youngest stage in my possession is shown 

 in surface view in PI. XIV, fig. S^and insectioninfig.9. The blas- 

 toderm forms a circular patch about '2 mm. in diameter, lying on 

 the surface of the yolk at the end of the egg nearest to the micro- 

 pyle, and consists of about twenty large cells, those in the centre 

 measuring about *03 mm. in diameter. In section (PI. XIV, 

 fig. 9) it is seen to be a single layer, the cells of which are 

 about '023 mm. thick in the centre. Round the margin the 

 cells are wedge-shaped so that the blastoderm lies flush with 

 the surface of the yolk. The cell-contents are coarsely granu- 

 lar, rather more so towards the lower side. The nuclei are 

 large, round and granular with distinct outlines. 



The yolk-spheres under the blastoderm appear to be breaking 

 down. The blastoderm and yolk are closely surrounded by 

 the structureless vitelline membrane (v. m.). This stage seems 

 to be a little younger than that figured in Metschnikoff's paper 

 in PI. XIV, fig. 6. 



Stage B. — In the next stage (PL XIV, fig. 10) the blastoderm 

 is somewhat larger, measuring •23 mm. in diameter. The 

 blastoderm is now almost twice as thick ("045 mm.). Some of 

 the cells are columnar, and occupy the whole depth of the 

 blastoderm, but the majority have divided in a plane parallel to 

 the surface, so that it is in places two or even three cells deep. 

 The nuclei vary in shape, those in the columnar cells being 

 oval. 



Stage C. — In the next stage (PI. XIV, fig. 11) the blastoderm, 

 now "3 mm. in diameter, is formed of an irregular mass of cells 

 showing as yet no trace of arrangement into layers. The cells 

 are comparatively small with well-marked outlines and large 

 nuclei. Round the margin of the blastoderm the cells form a 

 single layer on the surface of the yolk, but in the centre the 

 blastoderm is five or six cells thick, and the cells push their 

 way in between the yolk-spheres to which some of the cells 

 attach themselves. These cells, which attach themselves to 

 yolk-spheres, lose their definite outline and take, as far as I 

 have been able to ascertain, no part in the further growth of 



