OCTOPUS ARM, REGENERATION AND STRUCTURE iL 
the formation of the blood-clot, cannot possibly contribute cells 
for the tissues covering the wound. ‘The increase in the number 
of nuclei must be the result of nuclear division. In spite of 
careful search, I was not able to find any mitosis. The nuclei 
probably multiply by means of direct or amitotic division. 
The cicatricial tissue which is formed by the agglutinated 
blood-corpuscles is never cast off, but retained. The same 
may be said of the cicatricial tissue of the Pulmonata, Nudi- 
branchia, and Prosobranchia. Several authors have been able 
to establish the same facts for worms. ‘The wounds of the 
Vertebrata and the Arthropoda (with some exceptions), however, 
heal under a scab of coagulated blood. The scab soon degen- 
erates and is cast off as soon as the healing has been accomplished. 
In time the leucocytes, which constitute the cicatricial tissue, 
become more and more hyalin. The granules, which were at 
first equally “distributed in the protoplasm, gather around the 
nucleus and along the cell wall and finally disappear. The 
cells change their shape—formerly round, they now become 
elongated. At the same time the nucleus also becomes elongated. 
At times this alteration begins in the most superficial layers of 
the cicatricial tissue, but the study of a greater number of sec- 
tions showed that generally the most exterior cells retained their 
round shape longer than those below the surface, the latter 
becoming elongated very soon (figs. 20 and 21). These changes 
take place in the cicatricial tissue before it is covered by epi- 
thelium. MHescheler, Friedlander, and Rievel found similar 
elongated spindle-shaped cells in the cicatricial tissue of worms. 
Friedliinder and Rievel claim that these cells are evolved from 
leucocytes, whereas Hescheler doubts it. What finally becomes 
of this cicatricial tissue? There are two points worth notice 
in connection with it. In the first place, I was never able to 
find any sign of degeneration in this tissue, and, secondly, the 
regenerating epithelium does not grow under or through it, but 
covers it. Both these facts show plainly that it is retained and 
not cast off. It therefore may be calied a blastema, and in order. 
to distinguish it from the second blastema, which appears later 
and consists of neuro- and sarcoblasts (fig. 31), I would designate 
