Germ-Cells in Clirysomelicl Beetles. 283 



are no longer found on all sides of the cell, bnt are definitely directed 

 toward the entrance to the canal. This may be seen in a transverse 

 section of an egg of Lrpthwtarm similar to Stage 11 (Fig. 35). In 

 this figure two pole-cells are near the inner end of the pole-cell canal, 

 two are creeping along one side of the groove in the germ-band, while 

 three others are still in the amniotic cavity, evidently moving toward 

 the canal. A greater magnification brings out more clearly the shape 

 of the pole-cells and the direction of their migration. Fig. 56 shows 

 two of these cells taken from a transverse section (Fig. 38) of the 

 tail-fold of an embryo similar to Stage J. The psendopodia are 

 here unmistakable; they are extended toward the entrance to the 

 pole-cell canal. The hyaline cytoplasm at the tips of the psendopodia 

 resembles the ectoplasm of Amoeba; it will be recognized as the 

 vacuolated layer which was carried away from the "Keimhaut- 

 blastem," where the pole-cells were extruded from the egg (Fig. 21, 

 vac. St.). The pole-cells seem to be thigmotactic, few of them being 

 found free in the amniotic cavity ; they are usually observed close 

 to the germ-band or crowded one against another. 



Fig. 55 shows a pole-cell and an adjacent blastoderm-cell enlarged 

 from the sagittal section shown in Fig. 37. Here we find little or 

 no evidence of psendopodia. This is the -usual condition of the 

 pole-cells after they have reached the interior of the egg. Their 

 method of progression from this stage on is not easily made out. 

 In a later stage (Stage M) the germ-cells are partly surrounded by 

 mesoderm-cells ; their outline is still irregular, as is shown in the 

 enlarged draAving (Fig. 57), but no long psendopodia such iis are 

 present in the younger embiyos can be seen. It may be that the 

 pole-cells cease to move actively after they reach the interior of the 

 embryo, and that they are pushed into place by the rapidly prolif- 

 erating mesoderm-cells. 



3. The Origin and Early ILisionj of ilic Gevm-Cells in the Insecia. 

 No general statement can be made regarding the time and place 

 of origin of the primitive germ-cells in the Insecta, as the species 

 which have Ix-en examined represent only a small proportion of 

 the tvpes necessary fur a thorough understanding of this subject. 



