112 M. Oscar von Grimm on the Agamic Reproduction 



tlic 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 laminae are also 

 already to be seen. 



A little after the stage of development jnst described, a 

 longitudinal furroAv, the median vitelline ridge of AVeismann, 

 becomes perceptible on the inner surface of the germinal 

 streak, dividing the whole germinal sti-eak into tAvo germinal 

 imds. This is accompanied by the complete closiue 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 wliich the em- 

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

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

 amnion insectorumy Kupfer's emhryonal envelope ^ and Brandt's 

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

 bryonal envelope forms Metsehnikow's covering lamella (Deck- 

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

 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 embiyonal 

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

 shows itself through the ruptured place. "While tliis rupture 

 of the inner embryonal envelope enlarges, the germinal jx^ds 

 also increase in length, so that the furrow se]iarating 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 oti" the primitive an- 

 tenna. Then we also observe the fiu-ther development of the 

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

 pointed irregular segments. They have their points turned 

 upwards. 



Now also occurs the constriction of the cephalic segments, 

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

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

 seen at the commencement of the development, now becomes 

 visible. 



* The two together form the folded lamella of Weismami. 



