NOTOCRINUS VIRILIS. 49 



IV. NOTOCRINUS VIRILIS Mortensen. 



(Plates XXIV to XXVI.) 



The viviparous habit of this remarkable Crinoid was described in detail in 

 the author's memoir on the Crinoids of the Swedish South Polar Expedition. 33 



The eggs are 0.2 to 0.3 mm. in diameter. Quite a number of ripe eggs are 

 found at the same time in each ovary, while never more than 3 embryos 

 were found together in a marsupium, generally only 1 or 2. These facts 

 would seem to indicate that some of the eggs do not develop. In some cases 

 I have found in marsupia without embryos a yellow, coarsely granulated 

 substance which had decidedly the appearance of being eggs in disintegration. 

 The suggestion that some of the eggs are destined to serve as nourishment 

 for the developing embryos lies at hand. The unusual size of the embryos 

 would be naturally explained by this suggestion, while the size of the eggs, 

 which is by no means unusual, not larger than in Isometra vivipara, can not 

 account for this feature. 



All the embryos are at nearly the same stage of development; they are 

 found in various sizes, but there is no essential difference in their stage of 

 development; only in one case do I find the vestibulary invagination in a 

 much younger stage of development, being represented only by a slight 

 concavity along the ventral side, in which the ectoderm is considerably 

 thickened. Plate xxv, figure 8, is drawn from a series of sections of this 

 larva; it shows a young stage of the development of the glandular sacs (to 

 be mentioned below) not seen elsewhere. Otherwise this specimen is in the 

 same stage of development of the interior processes as the other larvae. This 

 circumstance, which is very unfortunate for the study of the successive 

 changes of the developing embryo, would seem to indicate that the eggs are 

 emptied into the marsupia a number at a time, as is the case with the Crinoids 

 with free eggs thus far observed, not one at a time and at any time, as in 

 Isometra vivipara. The reason for this exceptional feature in Isometra is 

 evidently the fact that the spermatozoa are accumulated in a sort of vesicula 

 seminalis in the ovary (perhaps through a copulatory act) and always ready 

 for fertilizing the ova, while otherwise in Crinoids the eggs are emptied only 

 when a male emits sperm, the sperm seemingly acting as a stimulus. 



As stated above, no eggs or very young embryos are found in the mar- 

 supia, so that unfortunately no information can be acquired about the 

 cleavage (which I would expect to find of the same type as in Isometra vivi- 

 para) or the first developmental processes. There is, in fact, only one larval 

 stage to describe, viz, the nearly fully formed larva; but this affords so many 

 novel features that considerable interest attaches to it. 



33 In "Wissensch. Ergebnisse d. Schwed. Sudpolar-Expedition 1901-1903," Bd. VI, 8, 1918, pages 

 6, 7, plates in and iv. 



