BY VERA IRWIN-SMITH. 237 



A vulva is usually present in specimens over 18 mm. long, but up to lengths 

 of 25 or 28 mm. the genital system, though develoi^ed, is generally not fully 

 mature. As with the males, the degree of development varies in individuals of 

 the same length. Many specimens of 18 mm. are still in the larval stage, and 

 specimens up to 23 mm. long in collection A, which appear to belong to this 

 species, show no trace of a genital system (Text-fig. 32). 



Interesting variations occur in the dimensions and disposition of the various 

 parts of the female genitalia,, and a large number of specimens of all sizes have 

 been dissected and measured in order to make a special study of them. 



The female genital system. 



Physaloptera antarctiea belongs to the group distinguished by Seurat as 

 "formes tetrahysteriennes," having four uteri. Like P. abbreviata and P. pal- 

 laryi, the division into the four branches is dichotomous, and the general forma- 

 tion of these and the other parts of the genital system is similar. The vagina 

 leads into a narrow cylindrical vestibule with thick muscular and cuticular walls, 

 which forms an ovijector. Upon this follows a dilated chamber, the reservoir, 

 leading to the common trunk, with walls lined by large polygonal epithelial cells. 

 This, after a short course, divides into two branches, which very soon divide 

 again, the four branches being continuous with the four uteri, which occupy the 

 greater part of the body. Each uterus terminates in a small bulb-like receptacu- 

 lum seminis, from which is given off a very narrow oviduct, with walls com- 

 posed of a single row of cells. This soon passes abruptly into the wider and 

 elongated ovary. 



Writers describing the female genital system in other species have usually 

 given definite measurements for the various parts of it, and have described their 

 exact conformation and disposition in the body, evidently on the assumption that 

 these are constant characters, and have some specific value. But, in P. antarctiea, 

 the examination of a long series of specimens has proved that in no two, even 

 among worms of the same size, are they alike. 



The striking- diversity which is found in the disposition of the terminal 

 portions of the system is illustrated in Text-figures 11-16. The vestibule is 

 usually sinuous, but may extend either straight back (Text-fig. 15) or straight 

 forward (Text-fig. 12) from the vulva, the reservoir continuing on in the same 

 direction (Text-figs. 12-14) or bending abi-uptly, and forming with the vestibule 

 a U-shaped loop either inverted or upright (Text-fig. 15). The common trunk, 

 in turn, may be bent back on the reservoir (Text-fig. 16) or continue in the 

 same direction as it (Text-fig-s. 12-13), so that the forking of the trunk occurs 

 anywhere from the level of the vulva to the maximum length of the tubes from 

 it, either anteriorly or posteriorly. All the various forms are found in adult 

 specimens of about the same size, so that they do not represent different stages 

 of gTowth. The disposition of the uteri, however, shows a certain uniformity 

 in general arrangement, in spite of the diversity in detail. 



Text-figure 11, of a 34 mm. specimen, represents a fairly typical ai-range- 

 ment. Here the division into the four branches takes place in the region of the 

 vulva, and two branches, one from each of the second forkings, immediately turn 

 forward and extend straight up, side by side, to a little distance in front of the 

 junction of oesophagais and intestine, where they bend abruptly and run back 

 parallel, straight down the ventral side of the body, to about a fifth of the body 

 length from the posterior extremity. The other two branches do not bend for- 

 ward at all, but almost immediately cross to the dorsal side of the alimentary 



