Germ-Cells in Chrysoinelid Beetles. 289 



H. That area of the egg tliroiigh which the pole-cells pass is not 

 closed hj the hlastoderm but becomes the pole-cell canal, through 

 which the pole-cells later migrate into the embryo (Figs. 33-40). 



•4. The blastoderm-cells which fail to cover this area form a 

 syncytium containing pseudoblastodermic nuclei ; these nuclei for 

 a long period lie just within the egg near the polc-ccU canal, and 

 finally disintegrate (Figs. 24-25 and 33-39). 



5. After their se})aration from the egg the history of the pole- 

 cells is as folloAvs : 



(1) The pole-cells are carried slightly forward un the ventral 

 surface of the egg by the contraction of the ventral plate (Fig. 29, 

 Stage E) ; (2) they sink into the posterior depression of the ventral 

 groove, which is the beginning of the posterior amniotic cavity (Figs. 

 33-34, Stages F-G) ; (3) they are carried along by the developing 

 tail-fold, which penetrates dorso-anteriorly into the yolk (Stages 

 H-K) ; (4) they migrate through the pole-cell canal into the embryo 

 by means of amoeboid movements (Figs. 35-40, 47, 56) ; (5) upon 

 reaching the interior of the embryo they separate into two groups, 

 which come to lie as a strand on either side of the body, in the last 

 two abdominal segments (Figs. 40, 47-49 and Stages K-L) ; (6) these 

 two strands become shorter by a crow^ding together of the germ-cells 

 (Fig. 41, Stage M) ; (7) each of the two germ-glands thus produced 

 acquires an epithelial covering of mesoderm-cells (Figs. 42, 50) ; 



(8) the germ-glands, situated as before in the last two abdominal 

 segments, are carried, by the shortening of the embryo, to a ventral 

 position on either side of the body (Figs. 42-43, Stages M-0) ; 



(9) by its lateral growth around the yolk, the embryo carries the 

 germ-glands to a point near the dorsal surface on either side of 

 the mid-intestine (Figs. 51-53, 43-45) ; (10) the sexes can be dis- 

 tinguished at this time by the shape of the germ-glands, that of 

 the male being dumb-bell shaped (Fig. 45), while the female repro- 

 ductive organ is pear-shaped, and shows the development of terminal 

 filaments (Figs 46 and 53). 



