4 MATHILDE M. LANGE 
santi (76) was the first to make the tentacle of the octopus the 
subject of a microscopical examination. The best paper pub- 
lished on this subject up to the present was written by Guérin 
(08). 
The arm of the cephalopod consists of four distinct parts: 
first, the skin or integument; second, the muscles; third, the 
nervous system, and, fourth, the vascular system. . 
The skin is composed of two layers, the epidermis and the 
dermis. The epidermis consists of a single sheet and is covered 
by striated cuticle. The nuclei of its cells are quite large and 
contain granules. The unicellular glands are more or less pear- 
shaped in comparison with the ordinary epithelial cells, their 
plasm contains fewer granules and they are much smaller. The 
dermis of the octopus arm consists of connective tissue, which 
surrounds the chief muscle bundle in equal thickness on all 
sides. It is permeated by many blood-vessels, by muscular 
and nerve strands, and also contains chromatophores and lumi- 
nous organs. 
The muscles of the arm can be divided into three distinct 
groups, viz., the central muscle bundle, the muscles of the suckers, 
and the muscles which serve as a connection between these two 
groups. The central muscle bundle consists of six longitudinal 
muscle strands, one transverse set of fibers, and six oblique 
or diagonal muscle strands. The musculature of the suckers 
consists principally of radiating fibers interspersed with circular 
muscles, the latter being more numerous in the musculature of 
the adhesive part than among the muscles of the sucking cavity. 
At the juncture of the adhesive part and the wall of the sucking 
cavity the circular muscles are especially well developed, forming 
a so-called sphincter. The connecting muscles connect the suckers 
with the central muscle bundle and also with the dermis (fig. 1). 
Ballowotz (93) made a closer study of the finer structure of 
the muscle fiber and found that it forms a narrow cylinder taper- 
ing at each end. This cylinder consists of spiral fibers and a 
granulated protoplasmic substance, which probably serves as 
a connection between the fibers and holds them together. 
