314 Transactions of the Society. 



The crown itself consists of pectinellae, disposed in a circle (or 

 perhaps in a spiral, describing a single turn), and set in a furrow 

 quite near the border of the truncated" extremity of the animalcule. 

 Inside this annular furrow the peristome field projects in the shape 

 of a flattened disc ; and this, with the surrounding border of the 

 furrow, is coloured a dark emerald green, nearly black when 

 seen under a low power. This dark extremity represents the 

 "ocular spot" observed in some marine Folliculinee. In reality 

 the cause of the coloration is a particularly dense accumulation 

 of those very small particles which have been spoken of as 

 secreted by the cytoplasm. 



The rapid swimming of the larvae may be continued for a 

 very long time, in fact in each case it lasted about thirty hours. 

 After that tlie little creature looks weak and sluggish, and moves 

 more and more slowly; its form becomes changed, more like a 

 flask ^vith elongated neck; and at last it rests, flattens on the 

 siibstratum, broadening into an oval shape. It remains a long 

 time unchanged; there is no movement, and the cilia half dis- 

 appear from sight; the pectinellpe which formed the crown dis- 

 integrate ; everything seems dead. 



But life is not extinct. After a time of rest which may last 

 for hours, the animalcule contracts, and the extreme limit which 

 it had delineated when flattened remains visible, like a very thin 

 pellicle encircling at some distance the newly acquired contour of 

 the animal (fig. 11). This pellicle is the new envelope. It is as if 

 the Folliculina when at rest after its long course had exuded a kind, 

 of varnish which hardened at once and remained where formed. 



The retraction inside the newly formed pellicle is, however, 

 not effected at the same moment in all parts of the body; the 

 " head," or crown-bearing anterior part, remains behind for a time 

 (fig. 11). Then the crown itself is seen to collapse, the pectinella^ 



DESCRIPTION OP PLATE II. 



Folliculina holtoni, 



Eig. 8. — A retracted individual in its shell. 

 M 9. —A specimen in course of transformation to the state of vermiform larva 



(the same as fig. 7, a few days later). 

 M 10. — The vermiform, free-swimming larva. 

 ,, 11. — First stage of the transformation into a fixed individual and first 



indication of a shell. 

 ,t 12. — A more advanced stage. 

 1, 13. — Details of the anterior part of the body at a somewhat more advanced 



stage. 

 ,, 14. — -A still more advanced stage, with distinct indication of a peristome. 

 ,, 15. — A further more advanced stage, in which the typical form of a (retracted) 



Folliculina is beginning to appear. 

 „ 16.— A specimen without any shell, contracted. 

 » 17. — Division ; the two individuals already separated, the young one, previous 



to its liberation from the shell, oval ; the old one somewhat cylindrical, 



with a new peristome already forming. 



