172 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



Meanwhile the neuroblasts have become evident and distinctly differ- 

 entiated from the adjacent cells which lie between the buds of the append- 

 ages (Fig. 78, neur). A neural furrow, however, has not been observed. 

 As development progresses, a peculiar form of blastokinesis occurs which 

 is neither a rotation nor a revolution. The ventral surface of the embryo 



lb 



Fig. 77. — Isotoma. Sagittal section of early embryo, (do) Dorsal organ, (eci) 

 Ectoderm, {gc) Germ cells, {it) Inner layer, {lb) Labium, {md) Mandible. (J,h) 

 Thoracic rudiments, {yc) Yolk cell. 



between the first maxillary segment and the first abdominal segments 

 becomes somewhat flattened and then begins to push into the yolk (Fig. 

 79) . By this time antennae and thoracic legs have increased in length, and 

 segmentation has begun. The mouth parts have increased in size, and 

 there appear between them the paired parts of the hypopharynx, the 



coel 



neur 



Fig. 78. — Isotoma. Cross section. (,cod) Coelome. (,ect) Ectoderm, {mds) Middle 

 strand of inner layer, {neur) Neuroblasts. 



superlinguae (paraglossae of Philiptschenko), which, however, are not 

 provided with a corresponding ganglion. On the first abdominal segment 

 there develops a pair of buds which later are modified into the tubus 

 ventralis. As in the other appendages, the mesoderm here fills the 

 evagination. The posterior part of the abdomen now also becomes seg- 



