$2 W. N. F. WOODLAND 
probable that in the Gecko tail the four sub- 
muscular fat bands must represent centrally- 
situated longitudinal unsegmented muscles 
which have degenerated into fat and become 
secondarily segmented for autotomy. It 1s also 
certain that the superficial muscles of the Gecko tail have 
become secondarily simplified and segmented in relation to 
autotomy. - 
PLANES OR LINES OF CLEAVAGE IN AUTOTOMY. 
The annular lines of cleavage in the skin are indicated 
(1) by the arrangement of the scales in the skin, a regular 
straight transverse row of scales bordermg each side of the line 
of cleavage (Text-fig. 2, A), and (2) by the presence of a hne 
of very thin transparent substance, devoid of pigment and 
other cells, separating the two straight lines of scales of adjacent 
segments. Apparently in this line of tissue the epidermis and 
dermis of the intescument have become extremely attenuated 
and practically reduced to a layer of non-cellular hyaline 
matrix, only occasionally traversed by capillaries and nerves 
passing from one segment to another. In the subcutaneous 
fat layer (Text-fig. 4, E) the lmes of cleavage are denoted by 
similar lines, alone composed of this non-cellular hyaline 
matrix and bordered by several rows of connective tissue cells, 
outside which lie the cells of the fat layer. Similar sheets of 
matrix separate the muscle segments of the tail and the seg- 
mented parts of the longitudinal fat bands (Text-fig. 2, C). 
With reference to the plane of cleavage dividing the middle of 
each centrum and neural arch, Gadow ? (p. 494) describes this 
as a ‘ cartilaginous septum ... which coincides exactly with 
the line of transverse division of the vertebra . . . where the 
tail breaks off and whence it is removed’. This is a mistake ; 
the vertebral plane of cleavage simply consists (Text-fig. 2, C), 
like the planes and lines of cleavage already mentioned, of 
a sheet of non-cellular hyaline substance which is continuous 
i The Cambridge Natural History. Volume on Amphibia and Reptiles, 
H. Gadow, 1909. 
