32 ILLINOIS BIOLOGICAL MONOGRAPHS [32 



uterus had almost attained its complete development. Those workers 

 who ascribe the production of these pouches to the crowding of the eggs 

 have evidently failed to read the evidence to be seen in the developing 

 uterus. Likewise those who ascribe the splitting of the proglottid down 

 the ventral side to the pressure of contained eggs have failed to note the 

 fact that the ventral pouches perforate the ventral side in one or more 

 places before the pressure of eggs is great enough to split the proglottid. 



The number of pouches on either side varies greatly but is reason- 

 ably constant for each species. Proteocephalus longicollis with its three 

 pouches (Fig. 167) on either side has the smallest number, while some 

 of the Ophiotaeniae (Fig. 101) have as many as thirty or more. When 

 filled with eggs the pouches in many species fill almost the entire ventral 

 field of the proglottid, while in some species of Ophiotaenia they appar- 

 ently take up but little more than half the width of the proglottid. The 

 pouches come to lie very close together, so that only small septa separate 

 them. Testes are pushed laterally or nearly obliterated by the pressure 

 of filled pouches. The vitellaria likewise are nearly obliterated in many 

 species while the ovarian lobes usually shrink considerably at this time. 

 The splitting of the ventral surface and the discharge of the eggs occurs 

 soon after. The wall of the uterus in its early stage of development 

 appears to be made of an epithelium the cell boundaries of which are 

 indistinct or invisible, altho the nuclei are very prominent and are 

 closely packed together. In the later stages of the uterus the nuclei are 

 farther separated, the outlines of the cells cannot be seen at all even 

 tho the membrane in which the nuclei lie is thick and apparently tough. 

 Riggenbach (1896:92) says, "Eine dicke Membran bildet die Wand des 

 ganzen Fruchtbehalters. Nach aussen lagern derselben stets viele kleine 

 Zellen auf, die zwar kein eigentliches Epithel bilden, wie es bei andern 

 Cestoden oft der Fall ist, jedoch als Reste eines solchen anzusehen sind." 

 In this view Riggenbach may be correct. 



The eggs usually have three membranes altho in a few species the 

 eggs have been recorded as having two membranes. In these cases it is 

 possible that a third membrane was overlooked. The outer membrane 

 of eggs that have been discharged into water is usually much larger 

 than the others. It is thin, hyaline and spheroidal in form. Eggs 

 preserved in utero and later examined do not show this membrane at all 

 prominently and in some cases it might easily be considered as a part 

 of the second membrane. The outermost membrane is smooth in out- 

 line. The only known exception is found in the eggs of Ophiotaenia 

 nattereri which Schwarz (1908) described as having peculiar branched 

 hooklets about its periphery. His drawing of this egg is reproduced 

 (Fig. 194). The middle membrane is usually thick and granular and 



