2i8 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 spealc 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 bi'own 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 



