6 TH. MORTENSEN, (Schwed. Südpolar-Exp. 
connective tissue, containing no calcareous corpuscles, fills out the interstices between 
the folds. 
The main interest, however, attaches to the genital organs, which lie almost 
wholly in the arms, not in the pinnules, as is otherwise the rule among Crinoids. 
The male genital organs are enormously developed, forming two alternate rows 
of conspicuous white bodies, joining closely in the middle line of the arm, and pro- 
ducing quite a swelling of the arm (PI. Ill, Fig. 4); they are ca. 4 mm. long, and 
look like small beans. There is a small pore, situated in the corner of the arm and 
the pinnule, on the distal part of the testis, through which the sperm is emptied 
(PI. Ill, Pig. 3; PI. IV, Fig. 5). The testes occur from pinnules 3 to 14. 
The enormous size of the testes — to which the species name virilis refers — 
must evidently have some relation to the viviparous habit of this species. That no 
copulation takes place may be concluded with certainty from the fact that no sper- 
matozoa are found anywhere in the marsupium or ovary of the female, as has been 
found in Isometra vivipara (see below p. 14). The spermatozoa, accordingly, have to 
find their way to the eggs in the marsupium through its small opening, which must, 
of course, involve some difficulty, so that this would appear to account for the un- 
usually large quantity of spermatozoa. 
The ovaries, which are much smaller than the testes, only ca. 2 mm. long, are 
likewise situated in the arms, at the base of the pinnules, but do not join in the 
middle of the arm (PI. Ill, Fig. 2). They are generally slightly concave at the distal 
side, where they abut upon the marsupium (PI. Ill, Fig. 2). 
The formation of the marsupium may be studied in the younger specimens. 
The first stage is represented in PI. IV, P'ig. 1 ; it is a fairly deep invagination of 
the skin, widened at the bottom. The further development simply consists in a 
widening of the sac (PI. IV, Pig. 2), which ultimately covers the whole distal side of 
the ovary; at first it has only a rather narrow lumen, but on the development of the 
embryos it widens very considerably, so as to occupy a considerably larger place 
than the ovary (PI. Ill, P'ig. 2; PI. IV, Fig. 4). The walls of the marsupium are at 
first strongly ciliated (PI. IV, P'ig. 2), especially in the middle part of the bottom, 
where the epithelium is distinctly thickened. In the fully developed marsupium this 
thickening has disappeared, and the ciliation also appears to have been lost. The 
opening of the marsupium remains unaltered, a deep, narrow pore, with a thick, 
ciliated epithelium (PI. IV, P'igs. 1, 2, 4). The pore is on a fairly distinct papilla, 
situated on a low elevation, like a small mammary organ (PI. Ill, P'ig. 1). It is 
thereby easy enough to distinguish the females from the males, in which the pore 
is not situated on any elevation. The female genital organs occur from the 3rd 
to about the 12th pinnule; probably it may extend still farther out in very large 
specimens. There is, in the female as well as in the male, no very distinct outer 
