ON THE LTFE-HISTOBY OF PEDIOELLINA. 259 



Whilst in the adult Loxosoma nothing comparable to the 

 formation of "brown bodies'' is known, the adnlt Pedicel- 

 lina has developed a special arrangement — the constriction at 

 the base of the calyx — by which the latter may be lost without 

 material injury to the remainder of the colony. 



In the adult Ectoprocta there seems to be the same 

 necessity for the rejuvenescence of some of the organs, but 

 here the occurrence of a thick ectocyst, usually intimately con- 

 nected with that of neighbouring individuals, in general pre- 

 vents the loss of any part of the body wall, as in Pedicellina. 

 In some of the stoloniferous Ctenostomata, however, the 

 entire zooecium is deciduous. 



But even in Pedicellina one may almost speak of a 

 ''zooecium'' in the same sense as in the Ectoprocta. It is a 

 well-known fact that septa occur at intervals across the stolon 

 of Pedicellina, and in most cases are developed in such a 

 manner that a piece of the stolon, connected with the base of 

 each stalk, is cut off from the remainder of the stolon by a pair 

 of symmetrically-placed septa. There are thus typically two 

 septa between the bases of each two stalks, and stalk-bearing 

 and stalkless sections of the stolon alternate regularly with one 

 another. 



It is thus possible to consider stalk plus portion of stolon 

 connected with it, the representative of a zooecium. The distal 

 end of the zooecium is from time to time segmented off, carry- 

 ing with it the whole of the alimentary apparatus, whilst a new 

 polypide is developed within the remaining portion by a process 

 of budding. By the formation of a new constriction the distal 

 part of the zooecium — the calyx — becomes again differentiated 

 from the proximal part — the stalk. 



In the Ectoprocta the occurrence of the same process is 

 usually obviously impossible, and the polypide alone degenerates, 

 forming a "brown body" which subsequently passes into the 

 new stomach, and is ejected by the anus. The occurrence of 

 this circumstance is already foreshadowed in two particulars in 

 Pedicellina. We find, in the first place, that a new polypide 

 is actually budded off bv the ectoderm of the zooecium at or 



