AVIAN CESTODES. “871 
into, the uterus. In other cases the diameter of the paruterine 
organ fluctuates from point to point, thus showing a less regular 
form such as is depicted in longitudinal section in text-fig. 7. 
This difference of form is probably to be explained by uneven 
contraction of the worm’s body or the muscular wall of the 
paruterine organ during preservation. The paruterine organ is 
long, but not quite so long as the uterus at which it ends. It 
therefore occupies rather less than half of the length of the 
proglottid. Dorso-ventrally the paruterine organ touches the 
limits of the medullary region of the proglottid; but laterally it 
does not fill up that space entirely, leaving some of the original 
medullary parenchyma visible right and left. There is no 
question of the inclusion of any organs in the paruterine organ 
such as I describe later* in what appears to be the equivalent of 
a paruterine organ in the Davaineid genus Otiditenia. The 
completely formed paruterine organ of this species of Rhabdometra 
is sharply marked off from the surrounding tissues by a layer of 
muscles disposed in circular fashion. 
The existence of such an outer muscular wall to the paruterine 
organ has been noted by other observers. I believe this layer to 
be adventitious and for the following reasons. In the younger 
stage just described there is no muscular wall at all; but the 
innermost of the transverse musculay fibres tend to follow the 
outline of the oval paruterine organ, though they hardly can be 
said to adhere toit. The contraction, or at least the alteration, of 
the form of the paruterine organ into a circle in transverse section 
would tend to further a close relationship between itself and the 
immediately surrounding musculature. In any case such a 
relationship exists. The shape in section and the general form 
of the paruterine organ together with its muscular coat are not, 
however, the only points in which the adult organ differs from 
the less perfected stages. The tissue which fills it is apt to have 
a concentric lamellar arrangement shown in text-fig. 8; this 
is also visible in sagittal sections but is not shown in text-fig. 7, 
since the latter is not of a sufficiently highly magnified preparation. 
It is shown, however, in text-fig. 6. 
In the younger proglottids (text-fig. 5) the paruterine organ 
ends up in close contact with the uterus, as has been already 
mentioned. It ends, however, in a definite border which is a 
straight line. In the completely developed paruterine organ 
there appears to be an absolute continuity, and the connective- 
tissue core of the paruterine organ melts away, as it were, in the 
cavity of the uterus. It appeared to me that the caleareous 
corpuscles, which are apt to be specially abundant on the paru- 
terine organ at its distal end though found throughout it, are 
both smaller in many cases and generally less abundant in the 
older paruterine organ, It looks as if they were used up perhaps 
by the growing embryos. Furthermore, the “ perforating ” dorso- 
* P. 880. 
