236 LUMPUS. [Vol. V. 



The apex of the posteriorly directed triangle, which was 

 described for the previous stage, has now become a broadened 

 patch, while the base of the triangle has given place to the 

 re-entrant formed by the disappearing blastoporic rim. Anterior 

 to the just described region of important events is spread a very 

 faint cloud with more or less irregular boundaries. Its outline 

 is deeply bifurcated anteriorly (Pel.), and laterally two exten- 

 sions are to be observed (An. 1 , An. 2 ) on either side. The large 

 U-shaped cloud of the previous stage has thus been compressed 

 towards the median line, as Reichenbach has described for Asta- 

 cus. Its free ends, though somewhat reduced in area, still pre- 

 serve their enlargements. Other portions of the egg show at 

 present no remarkable characters. 



After the hardened eggs have remained some time in alcohol, 

 the capsule, as usual, may be easily removed ; but there now 

 appears, for the first time, a second egg membrane, the "Blasto- 

 dermhaut." This membrane appears in irregular blisters, being 

 at first only partially sloughed from the underlying ectodermal 

 cells, of which it has hitherto formed a cuticle. The condition 

 of the " Blastodermhaut " at this time made the securing of 

 stained preparations extremely difficult, though a sufficient num- 

 ber of fragmentary preparations were made to demonstrate sat- 

 isfactorily the general arrangement of the nuclei and the method 

 of closure of the blastopore (PL XVI, Figs. 2 and 3). 



Compared with the immediately preceding stage the surface 

 nuclei are much more abundant, and certain definite centres of 

 aggregation are to be noted which follow, in the main, the out- 

 lines of the cloud-like mass already described. 



The nuclei are most abundant around the contracted lips of 

 the blastopore (PL XVI, Fig. 2, G.m. and Fig. 3, G.m.), which in 

 typical cases closes by the incurving of its hitherto somewhat 

 straightened anterior edge. The lateral edges of the opening 

 now approach each other, and become thickened at their inner 

 edge, where they are also more highly nucleated (Fig. 2, L.G.m.). 

 Externally they are separated from the surrounding ectoderm 

 by a slight depression. 



The first appearance of the third pair of cephalic appendages, 

 the jaws, is represented at PL XVI, Fig. 3, J, anterior to 

 which no remarkably differentiated portion of the ectoderm 

 is found until the procephalic lobes are reached, where two 



