54 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



zations. Connecting links and exceptions are certain to be found, espe- 

 cially among the smaller and more aberrant families. 



a. Lateral and dorsal sides of the egg covered by an envelope which represents the 

 amnion and serosa, the ventral face of the embryo not covered by either amnion 



or serosa during the course of development (Fig. 74) 



I. Myriapoda, Collembola {Isotoma), Diplura (Campodea) 



aa. Ventral face at least in part covered by either amnion or serosa, or amnion wholly 

 lacking and the serosa rudimentary (some ants), or parasitic or viviparous 

 forms in which the envelopes have a nutritive function. 

 h. Amnion wholly lacking, serosa rudimentary, represented by but few cells .... 



Some ants 



bb. At least one envelope more or less developed. 



c. Parasitic or viviparous insects in which the envelopes have a nutritive 

 fimction. 



d. Envelope a trophamnion (Fig. 263A) 



X. Parasitic Hymenoptera (Proctotrupidae, Chalcididae, Bra- 



conidae) 

 dd. Amnion and serosa present. 



e. No blastokinesis. Amnion and serosa disintegrate 



(?) Psocidae 



ee. With blastokinesis. 



/. Amnion and serosa rupture at revolution 



HesperoUenes; some Aphididae 



ff. Envelopes remain unbroken at revolution Hemimerus 



cc. Envelopes membranous, chiefly protective. 



d. Dorsal wall of the embryo represented by primary epithelium, the 

 cells forming a serosa-like covering; amnion present in rudimentary 

 form slightly covering either both cephalic and caudal ends as in 

 Melophagus or only the caudal end (Fig. 331). .XI. Muscoidea 

 dd. One or both envelopes fully developed. 



e. One envelope fully developed, the other absent or rudimentary. 



/. The amnion alone present (Fig. 226) Strepsiptera 



ff. Serosa present, amnion rudimentary or wholly lacking (Fig. 



2815) IX. Aculeate Hymenoptera 



ee. Two fully developed envelopes except in the Thysanura where 

 they open to the exterior. 

 /. Embryo drawn into a furrow {Machilis) (Fig. 34) or into a sac 

 which opens to the exterior by a pore (Lepisma) (Fig. 109). 



II. Thysamira 



ff. The serosa fully covers the egg below the chorion, the amnion 

 covers the ventral face of the embryo (Fig. 215). 

 g. Amnion and serosa fuse either at the head end or along the 

 midventral line, where a rupture occurs just before 

 revolution; after revolution a secondary dorsal organ is 

 formed in most cases. 

 h. No yolk between amnion and serosa before fixial revolu- 

 tion, at least in anterior half (Fig. 215) 



III. Orthoptera, Dermaptera, Neuroptera, Trich- 



optera, Coleoptera in part (Hydrophilus, Dytiscus, 



Tenebrio, Aleloe, Donacia), Meter optera in part 



(Corixa), Eutermes, and some Odonata 



