LIMNOCNIDA TANGANICiE. 
87 
In the primary series it extends about 3 mm. np to the 
exumbrella, but in the seventh and eighth series of tentacles 
the attachment is not visible. 
“ The basal portion of the tentacle is hollow, and its cavity 
is in direct communication with the marginal canal . ” 
The structure of the tentacular ectoderm must be described 
in detail. This layer consists of large flattened cells, which 
appear polygonal in a surface view (Text-fig. 1). Interstitial 
cells are absent from the whole ectoderm. 
The elongated nematocysts have a very definite arrange- 
ment, which differs in different regions of the tentacle. In 
the more distal parts these organs are arranged in groups of 
about thirty to forty on small projecting knobs of ectoderm, 
the latter forming transverse rings which are very conspicuous 
in a contracted tentacle. Each stinging-cell is provided with 
a cuidocil, and the longer axes of the nematocysts are perpen- 
dicular to the surface of the battery, the latter forming a 
powerful offensive organ (v. Text-fig. 1). 
As already observed by Browne (3) and Gunther (4) these 
nematocyst batteries are absent from the proximal regions of 
the larger tentacles. The reason for their absence is obvious 
to anyone familiar with the appearance of the medusa, the 
proximal embedded regions being protected by the over- 
hanging distal parts of the tentacles whioh are carried in a 
downward position. 
The important point to be noticed in this connection is that 
the stinging-cells themselves are not absent from these 
proximal portions of the tentacles ; they merely do not form 
batteries in this position. This is most clearly seen by 
focussing with a high power on to the surface of a tentacle- 
base, when a number of nematocysts can be traced at the 
bases of the large ectoderm cells close to the structureless 
lamella (Text-fig. 1). 
The orientation of these stinging-cells is very definite, the 
longer axes of the capsules being always parallel with the 
structureless lamella and the surface of the tentacles, not 
perpendicular to the latter as in the case of the functional 
