508 RICHARD EVANS. 



In the specimen represented in fig. 23 the uteri do not 

 cross one another ; consequently the embryo in the right 

 uterus is on the right side^ and the oue in the left is on the 

 left side. In the two specimens represented in figs. 22 and 

 23, there is another marked difference in the topography of 

 the uteri. In fig. 22 the uteri are packed under a loop of 

 the posterior end of the stomach, and do not extend forward 

 on either side of the alimentary system ; while in figure 23 

 they are placed on the right side of the stomach, and extend 

 forward as far as the first pair of legs. Tlie stomach in this 

 case has no loop at its posterior end, and this may be the 

 cause of the forward extension of the uteri. 



As has been stated above, the ovary is constant in its 

 position. The proximal ends, that is, the ovarian ends of 

 the uteri, always pass forwards to a greater or less distance ; 

 the middle portions are intricately coiled among them- 

 selves, and may form one or two loops round the stomach ; 

 the posterior ends descend and pass on the outer side 

 of the nerve-cords to the short vagina (Hgs. 22, 23, and 

 33). 



The thickness of the uterine wall is highly variable. It 

 may be thick and consist of a well-developed peritoneal 

 investment, a tunica muscularis, a tunica propria — which is 

 usually very thin, — and a lining of tall columnar cells 

 (figs. 51, 52, and 54), or it may be thin, when it seems to 

 consist of thin layers of cells. This difference, however, is 

 moi*e apparent than real, for it is due to the expansion of 

 the uterus brought about by the increasing volume of the 

 developing embryos, as well as the secretion of nutritive 

 material by the lining cells, and consequent diminution in 

 size. That there is no actual loss or destruction of the lining 

 cells is amply proved by the way the columnar cells which 

 line those portions of the uteri situated between the several 

 embryos gradually pass into the flattened layer which lines 

 the portions of the uteri in which the embryos are found 

 (fig. 53). 



In mature specimens the uteri contain a variable number 



