TOO 
2. The Mid-gut .—This extends from the level 
of the first pair of legs to the posterior border of the 
sixth abdominal segment. 
(i) An anterior narrow portion resembling an 
oesophagus. 
(ii) A posterior dilated portion at the level of 
the sixth (and fifth) abdominal segments in which, 
if the last meal of blood is not quite digested, a black 
mass will be seen. If any blood remains in this portion, 
i.e ., ‘ the stomach,’ discard the specimen for one 
kept longer without food, as it is otherwise very 
difficult to see zygotes. 
(iii) At the commencement of the mid-gut a 
ring-like, thickened portion (the proventriculus). It 
acts as a valve between the oesophagus and mid-gut. 
3. Malpighian tubules .—Passing between the 
mid-gut and the separated segments, note five 
brilliantly white threads—the malpighian tubules. 
4. Hind-gut .-—Between the malpighian tubules 
the transparent intestine which may exhibit active 
peristalsis. 
5. Oesophageal diverticula .—Attached to the 
proventriculus an exceedingly delicate membrane, the 
dilated oesophagus and three diverticula of the same, 
which usually contain gas bubbles. Schaudinn has 
shewn by adding baryta water to these bubbles that 
they are really carbonic acid gas. Further, also, the 
bacteria in these diverticula produce enzymes which 
are the cause of the ‘ irritation ’ of the bite, as may 
be shown by rubbing a diverticulum into a scratch on 
the skin. The salivary secretion as has been generally 
supposed has not this property. 
The ventral diverticulum extends as far back 
as the fifth abdominal segment. 
