BY R. J. TILLYARD. 415 



need to be tested by further experiments if an opportunity offers 

 itself — 



1. The Cephalic Heai't is probal)ly not a separate structure, but 

 simply a temporary formation in the (lesophagus. 



2. It pumps liquid blood (without corpuscles) from the "head- 

 vesicle," /.''., from between the pronymphal sheath and true 

 larval liead, via the larval mouth, into the oesophagus. 



'^. The consequent distension of the oesophagus, aided b}' 

 forward pressure of the midgut, enables the larva, (a) to lift the 

 pedicel of the egg, and (h) to burst the pronymphal sheatli dor- 

 sally on the head, 



4. The apparent two-chambered condition of this organ is pro- 

 bably due to the I'igidity of the ientoi-ial framewoi-k, which con- 

 stricts it while in operation. 



C. (JnK'ral (Section 4). 



1 . Deprivation of oxygen for the developing embiyo is effect- 

 ively brought about by removal of the vegetable tissues in which 

 the egg was lai<l, and restricti<m of the amount of water and 

 access of fresh air. 



2. Of twenty-eight embryos so deprived of oxygen, sixteen died 

 without hatching, six reached the pionymphal stage, and six 

 reached the true larval stage, but died soon afterwards. 



3. Eight embryos in eggs confined in small blocks of vegetable 

 tissue, but otherwise subjected to restriction of the amount of 

 water and access of fresh air, in the same way as those in "2, all 

 reached the complete larval stage, and showed little or no signs 

 of impaired health. 



4. The single embryo which h;id not undergone revei'sion, before 

 being subjected to the treatment described in 1, contiuncd fo 

 develop ivifhout reversiiuj, and finally emerged as a pronymph 

 " tail foremost." 



ii. Co7iclusions to he draivtt.fnmi Serftoti o, coiicerrbinii Zyiiojiferld 



larxHi'. 

 1. Rectal respiration is cari'ied on regularly antl \ igorously 

 during the first half-hour or so of larval existence. 



