Folllculina holfoni (S. Kent). 315 



disappear, and a pale ring is left, which appears greenish from the 

 amount of coloured particles left there, and from the border of the 

 ring are seen, diverging right and left, the two lines of the new 

 envelope ; later on, the ring itself hardens and becomes the aper- 

 ture of the shell. 



Later still the animalcule shows the beginnings of a more 

 complete organization (fig. 12). The fi^rst indication of the peristome 

 appears as a simple swollen ring bearing cross-strict where feeble 

 cilia are seen lazily vibrating. The swelling of the ring seems to 

 be due to an invagination of the border, but after a time the 

 invaginated parts turn out again. The ring is then no longer 

 swollen, but appears as a serrated circle, where one of the teeth is 

 larger than any other. This will afterwards grow into the special 

 crest or tactile appendage of the larger lobe. The pectinellse, few 

 in number and still very weak, are distributed in a ring a little 

 inside the serrated border (fig. 13). 



Occasionally the anterior part of the animalcule, or, more rarely, 

 the whole body, suddenly retracts, to lengthen very quickly again ; 

 and these sudden retractions, and some weak vibrations among the 

 pectinellffi or along the cilia which still invest the body, are the 

 only indications of life. 



About fifteen hours later, we find a change again (fig. 14) : the 

 animalcule has now contracted, and its anterior extremity is broadly 

 truncated at right angles to the long axis of the body, while 

 around the truncated end runs a circular furrow, bordered by a 

 crown of pectinellre of peculiar appearance, looking rather like 

 thick, short tongs firmly united together, so that the whole ring 

 has more or less the appearance of a single undulating membrane, 

 whose undulations follow each other like slow flames running along 

 the ring. On one side the tactile appendage is already conspicuous, 

 and contracts or expands alternately. 



A few hours more and the animalcule shows something approach- 

 ing the normal form of a retracted Folliculina. The broad anterior 

 field with its circular furrow has sunk down on one side, wdiilst 

 the tactile appendage has been raised on the other; the interior of 

 the peristome-ring begins to be hollow, and along the sinking- 

 surface new lines of pectinellffi appear (fig. 15). 



From that moment the development becomes more and more 

 complicated ; the peristome border lengthens, the lobes appear, 

 and the vestibulum sinks lower down. But my observations from 

 this point are very incomplete ; circumstances did not allow of at 

 least an hourly examination. And besides, two of the observed 

 specimens never reached the adult state ; the third attained it, 

 however, and lived ten days more, showing during the first seven 

 days fully expanded lobes. 



This last specimen had gone through its entire evolution, such 

 as just described, in the space* of thirty hours, whilst the two former 



