MONOGRAPH OF THE EXISTING CRINOIDS. 463 



ATTACHMENT OF LARVA AND ITS TRANSFORMATION INTO STALKED FORM. 



DESCRIPTION OF LARVA DP TO FIFTH DAY AFTER ESCAPE FROM EGG MEMBRANE. 



After a free-swimming existence lasting usually for only a few hours, more 

 rarely for two or three days, the larva attaches itself by means of the attachment 

 disk at the anterior end. 



In an aquarium this may be observed very readily, for the larvse will attach 

 themselves to almost anything, to the glass walls, to stones, to shells, and to various 

 parts of seaweeds; but they seem to avoid attaching themselves in places where 

 the water is agitated. 



It is easy to preserve the larvae together with the vegetable support to which 

 they are attached, when the base can easily be cut in sections and the details of 

 the attachment made clear. 



After fixation development progresses in different individuals at very different 

 rates, so that no general statement can be made as to the exact time when any 

 given process takes place. The difference, indeed, may be so great that it is 

 possible to find among larvae 110 hours old many which have not passed the 

 48-hour stage. 



This is in strong contract to the extraordinarily synchronous way in which 

 the earlier development takes place in the embryos of the same brood. 



As a result of the position of the attachment pit on the ventral side of the 

 anterior end of the body the young larva at first lies with its entire ventral side 

 almost in contact with the object to which it is attached. Simultaneously with 

 the differentiation of the body into calyx and column the larva elongates and raises 

 itself to a position with the major axis at right angles to the plane of its support. 



The erect attitude is, as a rule, first attained when the roof of the vestibule 

 has broken through, the tentacles have become extremely mobile structures of 

 considerable length, and the stalked larva appears capable of the independent 

 assimilation of nutriment. 



Directly after the attachment, when the vestibule is still on the ventral side, 

 the indications of radial structure are restricted to the five evaginations of the 

 hydroccele ring, the beginnings of the chambered organ, and the basals and orals, 

 though none of these have attained their ultimate position. 



But during the changes about to be described the pentamerous structure 

 becomes dominant, although the original median plane can always be determined. 



In the early fixed larva a cross section shows the bilateral symmetry dis- 

 turbed only by the parietal canal, which is confined to the left side, and by the pore. 



The vestibule first shows a radial structure when it has moved entirely onto 

 the free posterior end, while in the section of the calyx adjoining the column there 

 is even then no indication of a radial arrangement. 



The rays in the stalked larva are indicated by Seeliger with the numbers 

 I-V: Ray V stands in the median plane of the bilateral larva ventrally; that is 

 to say, the plane in which the last trace of the vestibular invagination has dis- 



