The President's Address. By A. D. Michael. 
17 
a general sketch of the anatomy of an Acarns. I found, however, to my 
regret, that the time at my disposal for reading it would not be suf- 
ficient for anything of the kind ; therefore, rather than put before 
you a mere dry catalogue of parts, I have thought it best to confine 
myself to a single system of organs. I have selected the nutritive as 
probably the most important; it divides itself into two parts, the 
mouth-organs and the alimentary canal. The former may be taken 
to be somewhat on the Insect-type, but, as in the Insecta, the same 
elements are so combined as to form a great variety of results. One 
important difference, however, between the two groups is immediately 
apparent. In the Insecta there are two pairs of maxillae : the one 
pair usually free biting or piercing organs, although often joined with 
other parts to form tubes or converted into lancets, &c. ; the other 
pair united to form the labium ; each pair bears its own palpi ; but in 
the Acarina there is only one pair, and these have coalesced to form a 
maxillary lip ; to which the name of “ labium ” is sometimes, hut in- 
correctly, applied. It must therefore be borne in mind when the 
word “ labium ” is heard in connection with the Acarina, that the part 
referred to is not the homologue of the labium in the Insecta, but of 
their maxillae. In most families of the Acarina the fusion of the two 
maxillae to form a lip is sufficiently complete for them to have lost all 
function and appearance of biting or piercing organs ; but in the 
Oribatidae, although the bases are united and form the lip, yet the tips 
are free and functional as crushing-organs. A very good example of 
this is to be found in the wood-boring Hoplophora, the well-known 
Box-mite, so called from its power of shutting its rostrum down upon 
its body like the lid of a box, and withdrawing all its legs and soft 
parts into the interior, so as to surpass a tortoise in its own line, be- 
cause a tortoise leaves some holes open, and a Hoplophora does not. 
These organs are still functional maxillae in the genus named, and 
form an interesting step between the free maxillae of so many insects, 
and the completely anchylosed maxillary lip of such a creature as 
Sar copies, which would not be suspected as having arisen from the 
amalgamation of two jaws were it not for comparison with other 
genera, and for the fact that even here some rudiments of the 
maxillary palpi still persist. Another maxillary lip among the 
Acarina which seems to me very interesting in this connection is that 
of Gamasus : here the character of biting-organs, which is preserved 
in the Oribatidae, is entirely lost ; the organ, which Prof. Berlese calls 
“ the hypostome,” is a lip, and a lip only ; but Megnin has pointed 
out that what may be called the accessory parts of the Insect- 
maxilla, viz. the galea, the lacinia, &c., are all well preserved and 
are very apparent, although entirely absent in the case of the 
Oribatidae. 
To this maxillary lip the palpi are articulated in the ordinary 
manner, and it must be remembered that there is only one pair, and 
that it is maxillary, not labial. They assume great variety of 
1896 c 
