610 MARGARET ROBINSON. 



best and easiest way of observing the minute embryonic 

 appendages is to study the embryos whole with simply their 

 shells removed. When this has been done sections can be 

 cut, and they are of great use in giving complementary and 

 explanatory evidence. The whole embryos were stained with 

 Delafield^s hasmatoxylin, the sections with Kleinenberg's 

 ha^matoxylin and orange. 



Description of the Stages. 



My observations were made chiefly on the two embryonic 

 stages which are described below. 



9 Stage A (fig. 1). 



At this stage one can see on the ventral surface of the 

 blastoderm : 



(1) The mouth which has the appearance of a semicircular 

 pore. 



(2) The clypeus lying in front of the mouth, and already 

 showing division into two lobes. 



(3) A rudimentary brain consisting of three lobes on either 

 side. 



(4) An incomplete nerve ring on which lies one pair of 

 post-oral ganglia. 



(5) Two other pairs of post-oral ganglia. 



(6) A large pair of procephalic lobes. 



(7) Four pairs of rudimentary post-oral appendages. 



(8) Markings or grooves showing divisions between the 

 segments in which the appendages lie. 



The nerve-ring, with its thickenings, is here very minute. 

 I have represented it (fig. 1) and them as being sliglitly 

 raised above the rest of the blastoderm. This is done to 

 emphasise their appearance. 



Heyiiions (1901), in his account of the development of 



