112 M. Oscar von Grimra on the Agamic Reproduction 



tlie cleaving of the blastoderm, contracting the vitellus con- 

 stantly more and more. 



The embryonal envelope is at this time bent round the ex- 

 tremities of the embryo, and now shows only one small fora- 

 men, the margins of which may be very well seen from the 

 ventral side of the embryo. The vertical laminee are also 

 already to be seen. 



A little after the stage of development just described, a 

 longitudinal furrow, the median vitelline ridge of Weismann, 

 becomes perceptible on the inner surface of the germinal 

 streak, dividing the whole germinal streak into two germinal 

 pads. This is accompanied by the complete closure of the 

 embryonal envelope, so that now the oval foramen is no longer 

 to be seen. The walls of this embryonal envelope, which 

 have even previously begun to divide, now, after the union of 

 their free margins, form two envelopes separated from each 

 other. One of these envelopes, which lies immediately be- 

 neath the chorion, forms a complete capsule, in which the em- 

 bryo lies freely. This capsule, which has been formed from 

 the outer wall of the embryonal envelope, is Metschnikow's 

 amnion insectoruvi, Kupfer's emhryonal enveloj^Cj and Brandt's 

 external emhryonal envelope ; the other wall of the entire em- 

 bryonal envelope forms Metschnikow's covering lamella (Deck- 

 blatt) , Kupfer's folded lamella^ and Brandt's inner emhryonal 

 envelope *. 



Somewhat later the germinal pads become segmented in the 

 middle of the length of the ovum ; the three pairs of primitive 

 jaws are formed. During this process the inner embryonal 

 envelope is ruptured at the head, and the fore part of the head 

 shows itself through the ruptm-ed place. While this rupture 

 of the inner embryonal envelope enlarges, the germinal pads 

 also increase in length, so that the furrow separating them 

 from each other now reaches only to the fore part of the head; 

 hence the so-called cephalic pad may now be distinguished. 

 The vertical plates, which must be regarded as the foundation 

 of the inner embryonal envelope, give off the primitive an- 

 tennse. Then we also observe the further development of the 

 jaws, but especially of the mandibles, which now appear as 

 pointed irregular segments. They have their points turned 

 upwards. 



Now also occm's the constriction of the cephalic segments, 

 the three pairs of jaws moving towards the upper half of the 

 ovum. The abdominal furrow, also, which is not unlike those 

 seen at the commencement of the development, now becomes 

 visible. 



* Tlie two together form the folded lamella of Weismann. 



