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TEXT-BOOK OF ENTOMOLOGY 



which separates from the dorsal wall of the primitive segments, 

 forms the outer or splanchnic layer of the rudiment of the mid- 

 intestine (spm, Figs. 539, F, 544, sp). What remains of the dor- 

 sal wall of the coelom-sacs after this separation joins the genital 

 rudiments and gives rise to the so-called terminal thread-plate 

 (Fig. 544, ef). The endodermal streaks, with the splanchnic layer 

 lying next to them, may now be considered as the rudiments of the 

 mid-intestine (Fig. 530, m, etc.). These are noticeable in the fol- 

 lowing stages by their considerable lateral growth; they spread 

 out over the upper surface of the yolk, around which they nnally 



FIG. 514. Cross-section through the abdominal region of a somewhat older primitive band of 

 Phyllodromia germanica : by, rudiment of the nerve-cord ; c, remains of the coelomic cavity ; 

 c.z, rudiment of the genital efferent passage ; ec, ectoderm ; en, endoderm : ef, terminal cord-plate ; 

 fk, fat-body tissue ; gs, genital cells ; h, rudiment of the heart ; p, rudiment of the pericardial 

 cavity; pa, rudiment of the pericardial septum ; so, somatic mesoderm layer; sp, splanchnic meso- 

 derm layer. 



entirely grow (Figs. 539, C-F, 544, 545). This growth around the 

 yolk goes on in most cases in such a way as to unite the two mid- 

 intestinal streaks in the region of the ventral median line with each 

 other. Then afterwards their union on the dorsal side takes place 

 (Figs. 539, F, 545). The yolk thus passes completely into the 

 interior of the mid-intestine, and with it the remains of the dorsal 

 tube or dorsal organ, when such an one is present. 



The salivary glands. These segmentally arranged glands, which 

 open by pairs into the three gnathal segments of the head, arise as 

 ectodermal invaginations originally opening not into the stomodseum, 

 but outwards on the surface of the body ; hence Korschelt and Heider 



