150 



ENTOMOLOGY 



FIG. 194. 



(Fig. 193), is the beginning, or fundament, of the hind gut. 

 At the anterior end of the germ band is a pair of large 

 procephalic lobes (Figs. 192, 194), which eventually bear the 

 lateral eyes, and immediately behind these are the fundaments 

 of the antennae. The fundaments of the primary paired ap- 

 pendages are out-pocketings of the ecto- 

 dermal germ band, and at first antennae, 

 mouth parts and legs are all alike, except 

 in their relative positions. Behind the 

 antennae (in Thysanura and Collembola 

 at least) appears a pair of rudimentary 

 appendages (Fig. 194, i) which are 

 tnought to represent the second antennae 

 of Crustacea; instead of developing, they 

 disappear in the embryo or else persist in 

 the adult as mere rudiments. In front of 

 these transitory intercalary appendages is 

 the mouth-opening, above which the 

 labrum and clypeus are already indicated 

 by a single, median evagination. Behind 

 the mouth the mandibles, maxillae and 

 labium are represented by three pairs of 

 fundaments, and in Thysanura and Col- 

 lembola a fourth pair is present to form 

 the superlinguae (Fig. 195, si), already re- 

 ferred to. Next in order are the three 

 pairs of thoracic legs (Fig. 194) and then, 

 in many cases, paired abdominal appen- 

 dages (Figs. 194, 196), indicating an 

 ancestral myriopod-like condition; some of these abdominal 

 limbs disappear in the embryo but others develop into abdomi- 

 nal prolegs (Lepidoptera and Tenthredinidae), external genital 

 organs (Orthoptera, Hymenoptera, etc.) or other structures. 

 The study of these embryonic fundaments sheds much light 

 upon the morphology of the appendages and the subject of 

 segmentation. 



Ventral aspect of germ 

 band of a collembolan, 

 Anurida maritima. a, 

 antenna; a l -a 5 , abdominal 

 appendages; i, intercalary 

 appendage; /, labrum; li, 

 left labial appendage; 

 m, mandible; mx, max- 

 illa; p, procephalic lobe; 

 pr, proctodaeum ; fi-t 3 , 

 thoracic legs. 



