OCTOPUS ARM, REGENERATION AND STRUCTURE 19 
contours of the body, occupying a place which would naturally 
be filled by the continuation of the longitudinal muscles. 
As the cicatricial tissue of the animals whose blood contains 
fibrinogen soon becomes scabby and is cast off, it is quite natural 
that most of the publications on the regeneration in vertebrates 
and arthropods do not give any great attention to the cicatricial 
tissue. This applies almost without exception to all the reports 
on the regeneration in arthropods. Among the many authors 
who have studied the regeneration of vertebrates there are a 
few who point out that not all of the cicatricial tissue is merely 
a preliminary covering for the wound, but that some of it at least 
is utilized for some future purpose. Aufrecht (’90), Billroth, 
and Rindfleisch claim that the leucocytes enclosed in this tissue 
are the origin of connective-tissue fibers. Among the more 
recent reports on this subject I should like to draw: attention 
to a paper published by Baitsell (16). This paper treats of 
the processes connected with the healing of skin wounds in frogs. 
Baitsell points out that the blood-clot formed by the coagulation 
of the blood acts as a kind of connective tissue for the time being 
by holding the edges of the wound together. He found that 
the coagulated blood formed a typical fibrin net. Later on this 
net was changed into a fibrous tissue, consisting of separate 
fibers and fiber bundles. This alteration was affected in a few 
days’ time. This change could not be traced to the activity of 
any other cells, as it took place before any connective-tissue 
cells had migrated into the blood-clot. The new tissue had the 
appearance of regenerating connective tissue. It soon ex- 
hibited the same reactions to staining agents as the old con- 
nective tissue, but differed from the latter in its attitude toward 
pancreatin, as it was digested by it. Baitsell points out that 
embryonic connective tissue is also digestible by pancreatic 
juice. The summary of all these reports shows that the theory 
according to which connective tissue is evolved from cicatricial 
tissue has already been advanced by several investigators. The 
blastema is separated from the subjacent tissues by a well-defined 
boundary line, only where it touches the musculature does this 
line disappear, and the tissues seem to pass into each other. 
