MONOGRAPH OF THE EXISTING CRINOIDS. 6)11 



stage is not entirely lacking, though it is probably very short, only long enough 

 to enable them to traverse the distance between the marsupium and the tips of the 

 cirri upturned between the arms to which they attach themselves. 



Dr. K. A. Andersson states that the development of the embryos of this specieb 

 in all essentials agrees with that of the embryos of Antedon. 



The immigration of the entoderm cells into the lumen of the gut begins much 

 earlier than in Antedon^ for it has already commenced when the invagination of 

 the vestibule begins, and long before the development of the embryo is completed 

 the gut is crammed with them, and its wall is quite without definite cell borders, 

 passing uninterruptedly over into the inner mass, which is very rich in yolk. 



In contrast to the usual conditions the vestibular invagination is deepest at 

 the anterior end, and its closure begins there. 



In two cases Andersson found larvae in which the posterior end had coalesced 

 with the wall of the marsupium which separates it from the genital sinus. He 

 suggests that possibly this is to assure better nutrition of the embryos; but Mor- 

 tensen says that this condition, which he was unable to confirm, must be decidedly 

 abnormal, and that it can have nothing to do with the nutrition of the embryos. 



AVlien fully developed, in which condition they resemble the corresponding 

 stages of Antedon, the larvse leave the marsupium through its slitlike opening. 

 After their escape they apparently attacli themselves immediately to the cirri 

 without passing through a true free-swimming stage. 



Since the arms as well as the cirri are movable, Andersson suggests that such 

 larvffi as are intercepted by the arms or pinnules are transferred to the cirri. 



NOTOCRINUS V1RILI8. 



In this species, according to Doctor Mortensen, the eggs are from 0.2 mm. to 

 0.3 mm. in diameter. 



As a number of ripe or nearly ripe eggs are found at the same time in the 

 ovary, while there are generally only one or two, rarely three embryos in each 

 marsupium, Mortensen believes that some of the eggs do not develop, but are 

 dissolved and possibly serve as nourishment for the embryos. In some cases ho 

 found a yellow, coarsely granulated substance in the marsupia, without embryos, 

 which had the appearance of eggs in process of disintegration. 



The embryos were found to be all at very nearly the same stage of develop- 

 ment. They are considerably larger than the embryos of any other crinoid, being 

 nearly 2 mm. in length. They possess no ciliated bands, and thus must be inca- 

 pable of swimming. 



ABNOKMAL EMBRYOS AND LARV.T5. 



Seeliger found that in some cases the first cleavage furrow divides the egg 

 into two cells, which are more or less markedly different in size. The second 

 furrow first divides the smaller, later the larger. The four-cell stage thus differs 

 from the normal in consisting of two larger and two smaller cells instead of 

 being composed of four of equal size. The third furrow is at right angles to the 



