AVIAN CESLODES. 869 
parenchyma and not an outgrowth of the generative system, is 
the existence of dorso-ventral muscle-fibres: these are not 
elements belonging to the paruterine organ and restricted to it, 
but, as is shown in the text-figure referred to, they arise outside of 
and perforate it. They pass into the paruterine organ at exactly 
right angles to the transverse diameter of the proglottid. A 
final characteristic of the paruterine organ at this stage is the 
Text-figure 6. 
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Transverse section through fully mature proglottid of Rhabdometra cylindrica. 
par. Paruterine organ. w.v. Ventral water-vascular vessel. 
larger number of calcareous bodies which lie within it and which 
are most numerous where it abuts upon the uterus posteriorly. 
Ransom has remarked upon the same feature in the paruterine 
organ of Sphyroncotenia. The shape of the paruterine organ at 
this stage as seen in horizontal sections is shown in text-fig. 5. 
In the longest, and therefore presumably ripest, proglottids the 
paruterine organ differs in some few particulars from its younger 
