216 MR. F. E. BEDDARD ON A 



particular series of proglottids (shown in text-fignre 25, p. 202) the 

 accumulation of interstitial cells was chiefly in the literal expan- 

 sions close to the water vascular vessels. In these regions of the 

 uterus the lumen was often entirely occluded by the densely 

 packed contents. In the uterus of a latei- stage — that which is 

 represented in text-figure 26 — the embryos were firmly imbedded in 

 the interstitial substance throughout the whole organ, so far as I 

 could see. This substance appears much denser in the uterus of 

 these older proglottids — so much so that cavities are left here and 

 there from which an embryo has fallen out in the course of 

 preparing the sections, which preserve exactly the spheroidal shape 

 of the embryo. The intei'stitial matter also seems to take stains 

 more readily at this stage, but exhibits no nuclei and no structure 

 that I was able to unravel. 



In the fully mature proglottids (see text-figure 30) this inter- 

 stitial substance is still present, and the embryos are seen in the 

 same way to be embedded in it, leaving cavities of exactly their 

 shape when they chance to have fallen out. The interstitial sub- 

 stance, however, appears here to be rather laxei' and is not so 

 deeply stained. It is very possible that this matter lying between 

 the eggs is a source of food-supply for the growing embryos. In 

 Avitellina centripunctata Gough has described the fact that the 

 eggs, after they have arrived in the uterus, " become surrounded 

 by smaller cells derived from the walls of the uterus," as has been 

 pointed out by Fuhrmann in the case of Stilesia sjustedti. These 

 cells are figured by Gough* as lying between and apparently 

 completely filling the interstices between the eggs. These cells 

 have conspicuous nuclei and are held by Gough to perform a 

 nutritive function with rega,rd to the eggs. 



This final disposition of the uterus, or perhaps rather of its 

 contents, in Otiditcenia ev.podotidis is not exactly like anything 

 that is known to me at first hand or from the figures and 

 descriptions of others. It is, however, suggestive of the figures 

 that have been published of Monopylidium and even of Davainea. 

 In his definitions of both of these genera (which are placed in 

 separate families) Ransom t describes the fate of the uterus in 

 almost exactly similar words : viz. " Uterus breaks down into 

 (numerous) egg-capsules, each containing one or more (several) 

 eggs." This is a little misleading in that the sharply contoured 

 and thick-walled capsules of certain species generally assigned to 

 the genus Davainea are diffei'ent fi'om the figures given of Mono- 

 pylidium infundihiduin etc. The definition would, moreover, 

 apply to Otiditcenia, in which, as I maintain, the conditions are 

 really rather diflferent from both. 



In several species of Monoptylidium the I'ipe eggs are scattered 

 and imbedded singly in the medullary pai-enchyma, so far 



* Gougli, Quart. Journ. Micv. Sci. vol. Ivi. pi. xiv. fig. 49. 



t " The Tsenioid Cestodes of North-Amencaii Birds," Bull. U.S. Nat. Mus. no. 69, 

 1909. 



