No. 382.] REVIEWS OF RECENT LITERATURE. 795 
Up to the present time the papers of Grassi (1884) and Biitschli 
(1870) on the development of the honeybee, contained nearly all our 
knowledge of hymenopterous embryology. The Hymenoptera are 
interesting as a highly specialized insect type, and the observations 
contained in Carriére’s and Biirger’s monograph are valuable because 
they enable us to appreciate more fully the peculiarities in the devel- 
opment of the more generalized insect orders (Apterygota, Dermap- 
tera, Orthoptera, Odonata, Hemiptera, etc.). It also appears that 
certain problems, such as the origin of the germ layers, can be 
studied, as Carritre and Biirger show, to greater advantage in the 
bee than in any other insects hitherto investigated, because the 
embryo always remains on the ventral surface of the egg, and is 
never longer than the egg, z¢., its posterior end neither curls over 
to the dorsal surface of the yolk as in Coleoptera, Diptera, etc., nor 
becomes imbedded in the yolk as in Hemiptera and certain Orthop- 
tera. Other advantages of a technical character are the liquid yolk, 
which is easily sectioned, the thinness of the shell (chorion), and 
the large size of the egg. These advantages have enabled Carrière 
and Biirger to make an accurate study of the formation of the germ- 
layers. Their conclusions are essentially the same as those published 
by Heider and Wheeler in their studies of Coleoptera (Hydrophilus 
and Doryphora). The entoderm arises from two widely separated 
regions of the blastoderm, one at the anterior, the other at the 
posterior end of the blastodermic groove which gives rise to the meso- 
derm. ‘The anterior entoderm rudiment sends back a pair of cellular, 
band-like prolongations under the mesoderm, while the posterior 
rudiment sends a similar pair forward. The prolongations of corre- 
sponding sides meet and then envelop the yolk by spreading dorso- 
ventrally. During this process the mesoderm is constricted off from 
the blastoderm in the mid-ventral line, and the stomodzal and 
proctodzal invaginations form, respectively, over the anterior and 
posterior entoderm rudiments. The formation of the stomodæum 
and proctodzeum is so closely associated with the origin of the two 
entoderm rudiments that one investigator, Heymons, has boldly 
denied the existence of an entodermal germ-layer in insects. Hey- 
mons derives the whole alimentary tract from the ectoderm (!). 
Biirger, however, very justly dissents from this view. He shows that 
the entoderm arises from the undifferentiated blastoderm, and that the 
stomodzal and proctodzal invaginations arise from the superficial 
layer of blastodermic cells, the only layer that can properly be called 
ectoderm. 
