130 Transactions of the Royal Microscopical Society. 
other hand, it is certainly, at first sight, difficult to understand 
why ants, having once acquired a sting, should allow it to fall 
into desuetude. There are, however, some considerations which 
may throw a certain light on the subject. The poison glands 
are much larger in Formica than in Myrmica. Moreover, some 
species have the power of ejecting their poison to a considerable 
distance. In Switzerland, after disturbing a nest of Formica rufa, 
or some nearly allied species, I have found that a hand held as 
much as 10 inches above the ants was covered with acid. But 
even when the poison is not thus fired at [the enemy from a 
distance, there are two cases in which the aculeus might be allowed 
to fall into disuse. Firstly, those species which fight with their 
mandibles might find it on the whole most convenient to eject the 
poison (as they do) into the wounds thus created. Secondly, if the 
poison itself is so intensified in virulence as to act through the skin, 
a piercing instrument would be of comparatively small advantage. 
I was amused one day by watching some specimens of the little 
Cremastoy aster sordidula and the much larger Formica cinerea. 
The former were feeding on some drops of honey, which the Formicas 
were anxious to share, but the moment one approached, the little 
Cremastogasters simply threatened them with the tip of their 
abdomen, and the Formicas immediately heat a hasty retreat. In 
this case the comparatively large Formica could certainly have had 
nothing to fear from physical violence on the part of the little 
Cremastogaster. Mere contact with the poison, however, appeared 
to cause them considerable pain, and generally the threat alone was 
sufficient to cause a retreat. 
Turning now to the internal anatomy, the brain in the social 
Hymenoptera is large and very complex. Its internal structure has 
been studied by Leydig * and more recently by Babl Buckbard t 
and Dietl. t From the lower and hinder margins of the sub- 
oesophageal ganglia, two commissures pass through the occipital 
foramen into the thorax, each segment of which has a ganglion 
of its own. There is also a small ganglion in the peduncle, and 
six in the expanded portion of the abdomen, corresponding w ith the 
number of the abdominal rings. 
The principal parts of the intestinal canal are the pharynx, the 
mouth sac, oesophagus, ventriculus, pylorus, duodenum, ilium, colon, 
and rectum. To it belong also the salivary glands and the mal- 
pighian vessels. The oesophagus, almost immediately after entering 
the swollen portion of the abdomen, expands into the ventriculus. 
Between the ventriculus and the abdomen is the pylorus, charac- 
terized by the presence of four flattened, leaf-shaped, chitinous 
plates. The posterior portion of the pylorus is sunk in the 
* Vom Bau des Thier-Kdrpers, 1S64. t ‘ Ar. f. Anat.,’ 1875. 
X ‘ Zuits. f. Wiss. Zool.. 1870. 
