Germ-Cells in Chiysomelid Beetles. 2Y7 



Canal der den Polzellen den Dnrclitritt ermoglichte." In his Fig. 

 55 several pole-cells are seen lying in the groove outside of the germ- 

 band, seveiial are present within it and a number are represented 

 half way through the opening in the ''Entoderm/' the "Polzellen- 

 canal." This migration of the pole-cells extends over a considerable 

 period. Escherich claimed that since the region of the ventral plate 

 containing the "Polzellencanal" later constituted a part of the 

 "ventrale Wand des Urdarmes, . . . somit ist es uns dadurch 

 moglich, die Mittelplatte als erste Anlage des Entoderm zu erken- 

 nen." In the last embryonic stage examined by this author, all of 

 the pole-cells had not yet completed their migration. 



I^oack (1901), in Calliyliora, also records the migration of the 

 pole-cells from the dorsal groove of the germ-band into the embryo. 

 This author, contrary to what Escherich found, could not satisfy 

 himself that a definite canal exists, but decided that the pole-cells 

 during their migration produce an adventitious gap in the ''Ento- 

 derm." Noack followed the history of the pole-cells until they 

 liecame scattered among the entoderm cells within the embryo. 



Lecaillon (1898) is the only author who has described pole-cells 

 in the Coleoptera. He states that after the "cellules sexuelles" are 

 separated from the posterior end of the egg they "ne restent 

 d'ailleurs pas longlemps en dehors de la masse ovulaire ; a mesure que 

 la segmentation progresse et que I'enveloppe blastodermique se com- 

 plete, elles commencent Ji rentrer dans I'oeuf . Pour cela, elles refoulent 

 le vitellus devant elles et s'insinuent entre les cellules peripheriques 

 dvi pole posterieur de I'oeuf, au fur et a mesure que celles-ci emergent 

 de la masse vitelline." A^Tien the blastoderm is finally completed, 

 the "cellules sexuelles" for a group "entre le vitellus et I'enveloppe 

 blastodermique," as indicated in his Eig. 10. In oidy one of the 

 species studied, Oastrophysa raphani. did a variation from this order 

 of events occur ; in this form the "cellules sexuelles," although tend- 

 ing to re-enter the egg, remain outside, as we have found the pole- 

 cells to do in Calligrapha and Leptinoiarsa. Their migration was 

 not carefully followed by Lecaillon in Gastropliysa. He found them 

 lying at the end of the posterior amniotic cavity, and shows two of 

 them in his Eig. 22, "dans le sillon profond qui se trouve sur le 



