ISO J. THOMAS PATTERSON. 



the ventral side of the intestine, and are intimately associated 

 with i he yolk glands, being surrounded on the dorsal and posterior 

 aspects by them. In a longitudinal section of almost any indi- 

 vidual in the egg-producing stage one can observe that the ova are 

 at their upper margins absorbing yolk from these glands, and while 

 the nutritive process may involve the ova of one half of the ovary, 

 yet it is much more conspicuous in the posterior third of that organ 

 (Fig. 9). At the extreme end of the ovary the absorption goes 

 on with great rapidity, the ova soon becoming gorged with nu- 

 tritive material. In consequence of this rapid growth certain 

 retrogressive changes involving the cell membranes separating 

 contiguous ova frequently make their appearance. As a result 

 two cr even more nuclei may come to lie within a common yolk 

 mass, which occupies the extreme tip of the ovary (Figs. 9, 10). 

 In other words, a syncytium is formed here. In the vast majority 

 of cases only two ova are involved so that the usual picture dis- 

 played in this region represents a binucleated yolk mass (Fig. 15). 

 It should be noted here that in this peculiar method of nu- 

 trition we have a mechanism alone adequate to account fully for 

 the reason why two embryos are habitually borne within a single 

 capsule. Just why two should appear is difficult to answer. 

 As a matter of fact, however, tw r o are not always present, for as 

 Linton has pointed out capsules are sometimes seen with three 

 embryos, and a few cases were noted by him in which only one 

 embryo is surrounded by the envelope. Furthermore, in the 

 figure of Nicoll referred to above, two capsules containing three 

 embryos each are clearly shown. In my own material several 

 cases of "triplets," including one with undivided eggs, have been 

 observed, as well as several with one embryo each. \Yhilc in 

 the light of these facts the twin condition in Graffilhi loses much 

 of its apparent significance, yet its appearance in the great major- 

 ity of cases made it necessary to undertake a careful study of 

 the histogenesis of the ovary in order to see if any mechanism, 

 other than that of the breaking down of intervening membranes, 

 could be discovered that would explain a potency to gemellipa- 

 rous reproduction on ihc part of that organ. At first it srrmrd 

 probable that a binucleated ovum was produced somewhere in 

 the oogonial history. A diligent search in the ovary fails to 



