408 E>tERGE?fCE OP DRAGOKFLY-LAftV.f;, 



fio-wanl moxenieiit of the midgut, would he quite sufficient to 

 cause the spHttiiig uf the pronyiuphal sheath, as well as the 

 lif ting-up of the egg-pedicel. 



As regards the twu-chambered structure of the cephalic heart, 

 a reference to the section in Text-fig. 2 shows the exact position 

 where the tentorium would cause a definite constriction in the 

 (csophajrus, if that organ were to distend itself in anv manner. 

 The i:>assage through this tentorial foramen, below the brain(/jr) 

 and above the suba?sophageal ganglion (soy) is small, and the 

 tentorial bars are hard aild rigid. Moreover, the oesophagus, 

 both at this point and throughout its entire length, is capable of 

 very great expansion, as may be seen in any tran.sverse section 

 of that organ, both by reason of the longitudinal pleating or 

 infolding of its epithelium, and the strength of it;- muscular 

 tunic. It seems reasonable to suppose that the division into 

 two chambers is caused by the tentorial compression. The notes 

 and drawings that I made for my previous paper show the point 

 of constriction placed somewhat further back than the position 

 of the tentorium. I think, however, that too much weight nuist 

 not be placed upon this fact, as it was manifestly impossible to 

 make accurate drawings of all the different parts of the larva, 

 during the single half-minute of vigorous struggle for emergence. 

 If, howevei', future observations should confirm my original 

 drawing's,* then there is reason to suspect the existence of a 

 special sphincter muscle at some definite position on the (eso- 

 phagus. Such a structure would have to be searched for in 

 transverse .sections. 



Section i. — The pjf'irt of nhnonna/ coudifivu.s upov I'lnhryoiiic 



development. 



We can now turn to some problems of a moi-e general nature 

 arising from the experiments described in Section 1. 



If we examine the table of results given on p. 398, we see that 

 Series B and C gave identical results, viz., in both cases all the 



* These will l>e found in V\^^.2A of my hook, "The Biology of Dragon- 

 tiles," shortly to he ]mhlishe(l hy the Camhridge University Press. 



