TRICHOPTERA AND LEPIDOPTERA 



335 



ectoderm cells (neuroblasts) on each side of the groove divide and later 

 give rise to the nerve cord. The compound eyes appear just before the 

 revolution of the embryo on the surface of the procephalic lobes as round 

 refractive areas, in which subsequently six dark-red pigment spots appear. 

 At this period the ectoderm shows a 

 thickened area in the region of the 

 eyes, which ultimately becomes con- 

 nected with the brain. 



Tracheae are formed in all the 

 postoral segments except the last 

 two or three segments of the ab- 

 domen. The spinning and salivary 

 glands are formed by ectodermic 

 invaginations on the inner side of the 

 second maxillae (labium) and the 

 mandibles, respectively. The Mal- 

 pighian vessels arise as six separate evaginations of the blind end of the 

 proctodaeum, a further increase in number being produced by budding 

 from the first three pairs. 



The mesoderm in a preceding stage had separated into segments, 

 the lateral extremities of which were formed of two irregular layers of 



am 



Fig. 289. — Neophylax. Cross section 

 through thorax before appendages appear. 

 {am) Amnion, {ch) Chorion, {il) Inner 

 layer, (ser) Serosa. 



Fig. 290. — Neophylax. Lateral view of 12-day embryo, {am) Amnion, {an) Anus. 

 {ant) Antenna, {ceph) Cephalic lobes, {ch) Chorion. {Ih) Labium, {md) Mandible, 

 (mx) Maxilla, (p 1) First thoracic leg. 



cells with no definite body cavity present. Later the mesoderm increases 

 in extent, and at the same time the cells composing it become less defi- 

 nitely and compactly arranged. The yolk becomes reduced in amount 

 and gradually recedes from the ventral plate. Into the cavity thus 

 formed amoeboid mesoderm cells migrate, giving rise to the blood cor- 

 puscles. As the yolk continues to withdraw from the ventral plate, the 



