Embryology. 941 
EMBRYOLOGY. 
ON THE PRIMARY SEGMENTATION OF THE GERM-BANDS OF 
Ixsrcts.?—Prof. Veit Graber summarizes his important results on 
the embryology of insects as follows :— 
1. The germ-band of insects is at first either discoidal (Steno- 
bothrus, Œcanthus), or is oblong (Hydrophilus, Lina, ete.). The 
primitive discoidal germinal area corresponds principally to the 
(Urkopf) antennal segment, since the (Urrumpf) primitive body 
as at first very limited dimensions. 
n most insects with an elongate germ-band, the primitive 
head-segment is also the first to be separated. An exception to this 
is found in Lina—if Hydrophilus is not taken into account—in 
which two transverse furrows appear simultaneously, forming three 
principal segments, which appear to correspond to the principal 
subdivisions of the insect body (head, thorax and abdomen). 
3. The primitive body (Urrumpf) of the germ-bands of Steno- 
bothrus and Cicanthus does not segment, as it has been assumed in 
the case in all insects hitherto, but before the permanent segments 
(metameres or microsomites) are established, the latter definitive 
segmentation is preceded by a subdivision into two and then three 
large segments (macrosomites). ` 
_ 4. Of these three primary segments (macrosomites) of the primi- 
tive body, the first corresponds to the sum of the jaw-bearing (gna- 
thophorous) metameres—gnathal macrosomites—the second, the sam 
of the limb-bearing metameres—thoracic macrosomites—and finally 
the third to the abdomen—abdominal macrosomites. i 
In the process of the primary or macrosomitic segmentation 
of the primitive body there is no external segmentation, that is 
transverse subdivision of the ectodermal plate, but a total segmen- 
tation of the inner (lower) layer, the hypo- (or ento-) blast. ao 
6. The secondary or microsomitic segmentation of the primitve 
body (segmentation of the microsomites into metameres) does not 
proceed in Stenobothrus and Lina (and also in spiders according to 
Morin), as is generally assumed, from before backwards, but it first 
involves the middle or thoracic (Ursegment) macrosomite. 
e may finally inquire as to the morphological significance of 
the primary subdivision into four or tetramerism of the germ- 
bands of Stenobothrus and Œcanthus. 
! Edited by Prof. John A. Ryder, Univ. of Penna., Philadelphia. 
* Uber die rimäre Segmentirung des Keimstreifs der Insekten. 
aapa. Jahrb xiv. Hft i 1888. Pp. 345-368, pls. xiv.-xv. Von V. 
T, 
