AVIAN CESTODES. 865 
shape, in transverse sections, of a parallelogram with rounded 
angles. The most important point in the development of this 
organ is that it is wholly unconnected with the uterus. The 
paruterine organ is found in proglottids where there is as yet no 
trace of a uter us. 
There can, therefore, be no comparison with the paruterine organ 
of such a form as Avitellina, ‘‘ where the uterine wall cells... . 
supply the origin of the egg-pouches or paruterine organ” *, With 
reference to species of Ahabdometra, the statements of Ransom 
are not definite. In the case of Rh. nullicollis, that author writes t 
that ‘the parenchyma in front of the uterus becomes dense and 
fibrous and develops into a prominent paruterine organ, which 
behind is in immediate relation with the anterior end of the 
uterus.” Of the paruterine organ of 7h. similis = he writes no 
more positively. We may infer from Mr. Ransom’s descriptions 
that the paruterine organ does not appear before the uterus and 
that it may be an outgrowth of its anterior wall. In this case 
there is an important difference from the species described in the 
present paper, and in any case there is a difference in time of 
appearance. 
The earliest appearance of the paruterine organ under a high 
magnification is shown in text-fig. 3. It consists mainly in an 
apparent multiplication of the nuclei of the medullary parenchyma. 
In any case they are more closely aggregated for a short region 
in the middle of the anterior half of the proglottid. This dense 
mass of nuclei—that is dense comparatively speaking—reaches 
forward to the anterior border of the proglottid. But it must be 
borne in mind that the actual delimitation of successive proglottids 
cannot be fixed unless the wall of the transverse water-vascular 
tube fixes it. In this case the paruterine organ does not reach 
the anterior limit of the proglottid in which it les. In more 
mature proglottids, however, the anterior margin of the par- 
uterine organ is so straight a line that one cannot help thinking 
that this may be the anterior margin of the proglottid, im which 
case the posterior wall of the transverse water-vessel lies within 
the segment in front. 
I have no evidence whether the great multiplication of the 
numbers of the nuclei to form the beginnings of the paruterine 
organ is due to an actual multiplication, or to a crowding together 
by simultaneous migration inwards from other quarters. The 
nuclei of the future paruterine body show no difference from the 
surrounding nuclei of the medullary parenchyma. I have said 
that the multiplication of the nucleiis the main feature of the 
paruterine organ on its first appearance. The only other 
difference from the surrounding parenchyma is a slight opacity, 
which is, I am convinced, simply due to the crowding of the 
nuclei. The network structure of the medullary parenchyma is 
not at first at all altered in the future meme organ. The 
* Gough, Q. J. Mier. Sci. lvi. p. 375, 1911. { Loe. cit. p. 34. 
+ Bull. U.S. Nat. Mus. No. 69, p. 29, 1909. 
