246 
PROGRESS OF MICROSCOPICAL SCIENCE. 
or the cavities in which they lie. In the human skin especially, these 
cells of the connective tissue are numerous and in intimate relation- 
ship with the superficial blood-vessels, but prominently absent from 
the collecting lymphatic channels lying alongside of these vessels, 
thus supporting the hypothesis they formerly emitted, that these cells 
were merely links in a nutritive chain, not radicles of tbe lymphatics, 
even when, as in tendon, the cornea, &c., they are connected with 
the lymphatics. The paper is illustrated by about a dozen and a 
half of camera-lucida drawings of microscopical specimens in their 
possession. 
The Imaginal Disks of Insects. — A most important work on the 
metamorphoses of insects has recently been published at Warsaw, by 
Professor M. Ganin. This work has been reviewed at considerable 
length in the ‘American Naturalist’ (July), doubtless by Mr. A. S. 
Packard, jun., the highest American authority on the subject. From 
this notice we take the following quotation of the words of M. Ganin 
with respect to the imaginal disks of insects : — “ I deem it proper to 
examine here the question of the morphological importance of the 
imaginal disks of insects in general. The data respecting their 
embryology and comparative anatomy render it very probable that the 
thoracic imaginal disks, hidden in the body of Muscidce, the thoracic 
imaginal disks placed immediately on the skin of Corethra, Miastor , 
and the Hymenoptera, and the thoracic legs of the larvae of Lepi- 
doptera and Coleoptera, are homological formations, replacing each 
other in all those groups. In other words, and more explicitly, I 
believe that the thoracic imaginal disks of the Hymenoptera, Muscidce, 
Corethra, and Miastor are nothing but reduced ambulatory legs, which 
in other insects (Lepidoptera and beetles) are used as organs of pro- 
gression, but in the above-mentioned groups (Muscidce, &c.) have lost 
their physiological value, and have preserved in the history of their 
development a mere record of that value. This view may be sustained 
by the following scientifically pregnant facts : 1. All insects, the 
larva) of which possess, in their thoracic segments, the so-called 
imaginal disks, do not have any rudiments of legs on the same seg- 
ments during the period of their embryonal development ; in other 
words, the imaginal disks take the place of the legs, which, in other 
insects, appear much earlier, in the same places, during the period of 
the embryonal development. 2. In insects, the larvm of which pos- 
sess thoracic legs, these latter are transformed into the legs of the 
imago, in such a manner that the final segmentation of the joints of 
the leg of the imago appears more or less sudden and simultaneous, in 
consequence of the segmentation of the corresponding leg of the larva, 
which has been very much drawn out in length. On the contrary, 
those insects, the larvae of which, instead of thoracic, ambulatory legs, 
have imaginal disks, show, before the appearance of the final segmen- 
tation of the leg of the imago, a stage of a provisional segmentation of 
the leg in the developing imago. Thus the segments of the leg of the 
imago of Muscidce, Hymenoptera, &c., do not all appear simultaneously, 
but gradually, first one, then two, three, &c. This provisional segmen- 
tation of the leg, growing out of the imaginal disk, must be considered, 
