128 
Wisconsin Academy of Sciences , Arts and Letters. 
of the glandular hypodermis. The great extent of surface of the hypoder- 
mis compared with that of its cuticle may indicate that during protrusion 
the latter is stretched and attenuated, thus allowing the secretion of the 
glandular cells to transude more readily. 
I have made no observations on the use to which the organ is put by the 
living animal. The observations of Lubbock and De Geer quoted above, 
render it probable that Anurida maritima uses its collophore as a sucker 
wherewith to fasten itself to the surface of the stone while the water is 
rising and falling. It probably does not leave its place of concealment 
during high tide to move about on the surface of the water like some of 
our inland species. As its body, like that of most other species, is not 
readily wetted, the layer of air that would cover it when emersed might 
be sufficient for respiration till the returning ebb. 
The collophore of Anurida , may be readily reduced to a pair of append¬ 
ages applied to each other in the median ventral line. The median in¬ 
duplication of the hypodermis and the corresponding single infolding of the 
cuticle I take to represent all that remains of the originally wide sternal area 
separating the two appendages. Sections through the more complicated 
collophores of a few of our common Podurids have convinced me that 
these organs are also reducible to the simple pattern of a pair of appenda¬ 
ges more or less closely united in the median line. I have not, however, 
made a sufficiently extended study of the more complicated types to be 
able to explain the manner in which their different parts originated. It is 
to be hoped that some investigator will in the near future subject these 
interesting organs to a rigid comparative examination, from both an ana¬ 
tomical and physiological standpoint. Ryder's observations on the embryos 
of Anurida maritima , together with the observations I have presented on 
the adult of the same species, render it very probable that the Collembolan 
collophore is to be regarded as a pair of appendages homologous with the 
pleuropodia of the lieterometabolous insects. 
It seems, moreover, not improbable that the collophore of the Collem- 
bola may have been derived directly from the pleuropodia of primitive in¬ 
sects. Originally a pair of protuberances, covered with a sticky, perhaps 
malodorous secretion, these appendages may have come to be of assistance 
as adhesive organs in such leaping species as had rather weak limbs and 
lived where they found it of advantage to alight on surfaces of different 
inclinations. 
Milwaukee, December 20th, 1889. 
