Germ-Cells in Chrysomelid Beetles, 253 



les cellules sexuelles se trouveut groupees . . . entre le vitellus 

 el" I'enveloppe blastodermiqiie." At the end of segmentation, the 

 germ-cells were found pressed against the inner surface of the germ- 

 band, just in front of the posterior end of the egg; here they remained 

 during the formation of the mesoderm. After the mesodermal 

 somites were completed, the germ-cells penetrated into them, and 

 formed two cylindrical groups, the germ-glands. These were then 

 carried by the lateral growth of the embryo to a point near the 

 median dorsal line. 



The above described processes also took place in Chrysome-la 

 menthastvi, Lina populi and L. tremulw. The primitive germ-cells 

 of Gastrophysa arose as in Clytra, but many of them remained out- 

 side of the egg and w^ere later found in the posterior amniotic cavity, 

 "dans le sillon profond qui se trouve sur le milieu de sa parol in- 

 terne. Avant la fermeture du sillon, les cellules y penetrant et scs 

 trouvent ensuite en dedans de la couche ectodermique." N^o observa- 

 tions were made by Lecaillon upon the precocious appearance of the 

 germ-oells in Agelastica alni. 



Several species of Chrysomelid beetles were studied by Friederichs 

 (1906). This author discovered that the cleavage nuclei in Donacia 

 crassipes reached the posterior later than the anterior end of the egg ; 

 the reverse is the rule in species of allied genera. After the blasto- 

 derm was formed "an der Ventralseite unmittelbar seitlich vor dem 

 Pol, findet eine besonders lebhafte Zellvermehnmg statt, so dass 

 einzelne Zellen aus dem Blastodermverband heraus und ins Innere 

 gedrang-t werden." These, the primitive germ-cells, were not very 

 different in Donacia from blastoderm-oells, but in Timarcha nicceends 

 and Chrysomela marg'mata they were distingiiished by the larger 

 size and darker color of their nuclei. The blastoderm (Ectoderm) 

 became interrupted at the point of origin of the germ-cells, an in- 

 vagination being found similar to the "Geschlechtsgrube" of Orthop- 

 tera (Heymons, 1895). The germ-cells remained just inside of this 

 groove; by the lengthening of the embryonic rudiment they were 

 carried to a point near the mid-dorsal region of the egg. Here they 

 were found at the end of the tail-fold, lying between the ectoderm 

 and the volk. The germ-cells, as well as the other cells of the embryo, 



