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Transactions of the Society . 
another much smaller opening anterior in position ; and that a perfectly 
plain hind-gut, quite different to the Malpighian organ, runs from the 
ventriculus to this second opening. There is no doubt of the existence 
of the small second opening in Hydrodroma, for Haller also has figured 
it. If Schaub be correct in saying that a hind-gut runs to it, there is 
an end of the theory that the Malpighian organ is the homologue of 
the hind-gut; but no one except Schaub has Over recorded seeing 
this second hind-gut in any of the great Tro mbidium-growp, where 
alone the difficulty exists ; and it is not the only point in Schaub’ s 
paper where he differs from all other Acarine anatomists. The strangest 
part is that, a year later, Schaub published a second paper on Ponta- 
rachna, another of the Hydrachnidae ; in it he drew and described a 
single opening only, the ordinary one, which he called the anus, just 
as other writers had done, without saying what viscus ran to it, or 
what was its connection, if any, with the mid-gut. 
Finally, the question arises whether we ought to consider, as we 
ordinarily do, that for the mid-gut to end blindly and not be in com- 
munication with any anus is something so utterly against the course 
of nature, as to be entirely incredible, even in animals like Trombidium 
and the Hydrachnidae, which live entirely by sucking the blood of 
other creatures. It is certain that Spiders and Gamasids live in the 
same way, and yet have a functional hind-gut, and there is a tradi- 
tion that Prof. Owen, when presiding over a meeting where some one 
described a creature with an alimentary canal that ended blindly, 
suggested that doubtless there was blindness somewhere, but it was not 
in the alimentary canal of the animal. On the other hand, some para- 
sites which live constantly bathed in the blood or wholly assimilable 
fluids of their hosts, do not possess a functional anus. Swammerdam 
figured the alimentary canal of the bee-larva as continuous, yet recent 
eminent writers, Dohrn, Leuckart, and others, have denied this, and 
assert it to consist of a mesenteron opening only by the oesophagus 
and entirely disconnected from the proctodaeum. Dohrn extends the 
observation to larval ants, and although Lowne is inclined to differ 
as to the precise stage of the life-history at which this occurs, yet it 
seems fairly well established that there are considerable periods iu the 
existence of some immature Hymenoptera, Neuroptera, and Diptera, 
when the alimentary canal is not continuous from mouth to anus ; it 
may therefore be just possible that in the Trombidium group, that 
condition may persist to a later period, it being a case of creatures 
living entirely upon assimilable fluids and not requiring to pass solid 
dejecta. 
