6 TH. MORTENSEN, (Schwed. Siidpolar-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 

 (PL III, Fig. 3; PL 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 Isoiiiftra 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 (PL III, Pig. 2). They are generally slightly concave at the distal 

 side, where they abut upon the marsupium (PL III, Fig. 2). 



The formation of the marsupium may be studied in the younger specimens. 

 The first stage is represented in PL IV, P'ig. i ; it is a fairly deep invagination of 

 the skin, widened at the bottom. The further development simply consists in a 

 widening of the sac (PL IV, P'ig. 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 ovarj' (PL III, Fig. 2; PL IV, Pig. 4). The walls of the marsupium are at 

 first strongly ciliated (PL IV, Y\g. 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 (PL IV, Pigs, i, 2, 4). The pore is on a fairly distinct papilla, 

 situated on a low elevation, like a small mammary organ (PL III, Pig. i ). 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 



