2 l8 
The Ohio Naturalist. 
[Vol. VIII, No. 2, 
that time a number of experiments and observations conducted 
during last summer, as well as the extremely interesting facts 
presented before the section of Experimental Zoology of the 
Seventh International Zoological Congress in Boston by Dr. 
Prizbram, seem to offer a proof of the idea that the mutilated 
organism as a whole partakes in the regeneration of a lost organ. 
I wish to speak here mainly of my observation on the com¬ 
pensation which takes place in case of posterior regeneration in 
Podarke obscura. This is a small marine polychaet, found 
abundantly at Woods Hole, in the Eel-pond on sea-weeds. The 
worms have a chitinous layer over their dorsal surface, the color 
of which grades from seal-brown to a very light shade of yellow, 
but in a few exceptional cases it is entirely wanting. 
If the posterior half of the worms be removed, a new tail will 
regenrate in course of some eight days. This regenerated tail 
will be as a rule devoid of any chitinous covering, and the tissue 
will therefore be quite translucent. This regenerated tail will 
soon, however, acquire a chitinous layer over its dorsal surface, 
which will gradually increase in thickness. As this process of 
thickening is going on the translucence of the newly regenerated 
tissue is being lost, and the covering also becomes darker and 
darker. 
The interesting thing to be observed in this connection is, 
that while this surface layer is formed on the regenerated tail, 
another phenomenon exactly opposite to the one just described 
occurs bringing about a gradual thinning out of the chitinous 
layer over the dorsal surface of the old piece. This gradual 
thinning out, which results finally in a complete exposing of the 
underlying tissues beneath, may start either on the part of the 
old piece nearest to the regenerated tail, or on the part furthest 
removed from it or even on the left and right sides of all the old 
segments. 
These two processes, the thinning out of the chitinous layer 
on the old tissue, on one hand, and its thickening on the regener¬ 
ating tissue on the other hand, will continue until both parts, 
the old and the new are covered by a continuous layer of uni¬ 
form thickness. The process, however, may not be brought to 
an end even at this stage, and go on until the dorsal covering on 
the new tail would become much thicker and consequently darker, 
than that on the old part. This shifting of the chitinous mate¬ 
rial from the old over to the new part will proceed still further, 
ultimately leading to the formation of a seal brown covering 
over the new, regenerated tissue and leaving entirely naked so 
to speak the old tissue. This condition is exactly the reverse 
of that with which we started when the old part was all coated 
with a seal brown layer of chitin, and the regenerated part was 
all naked. First the old tissue was thickly clothed with chitin, and 
