74 



MOLLUSCOIDEA. 



ing to Fr. Miiller there is in Serialaria a so-called colonial nervous 

 system which connects the individual zooids of one colony and enables 

 them to co-ordinate their activities. Claparede * describes the same 

 for Vesicularia, also for Scmpocellaria scruposa and Eugula (avicu- 

 laria). Special organs of sense have not been recognised. 



Many forms of Bryozoa present examples of a well-marked poly- 

 morphism. In Serialaria and its allies the joints of the stalk 

 represent a special form of individual ; they have a considerable 

 size and a simplified organization, and serve as the ramified sub- 



stratum on which the nutritive individuals 

 are placed. In addition, there are here and 

 there joints of the roots which, under the 

 form of tendril- and stolon-like processes, 

 serve to attach the colony. The peculiar 

 appendages known as avicularia and vibra- 

 cula, which are modified individuals and 

 seem to have the function of food-procuring 

 organs, are found in many marine Bryozoa. 

 The avicularia (fig. 547, Av) resemble birds' 

 heads and consist of two-armed pincers, 

 which are attached to the colony near the 

 openings of the cells and occasionally snap. 

 They may seize small organisms, e.g., worms, 

 and hold them till they are dead ; the de- 

 composing organic remains are swept into 

 the mouth by the currents caused by the 

 cilia of the tentacles. The vibracula have 

 a similar arrangement, but present in place 

 (after Busk). Te, Tentacular o f t } ie snap pi n g b e ak a long and extremely 



crown ; R, retractor muscle ; 



D, alimentary canal ; F, funi- moveable flagelliforni filament (fig. 548). 



Knal ] y there are the Ov icell8 (ooecia), each 



of which is filled with an egg; they have 

 the form of helmet or dome-shaped appendages and are sessile on 

 the zooecium (fig. 547 Ovz). 



The reproduction is partly sexual and partly asexual ; in the 

 latter case it may be effected by the so-called statoblasts or by 

 budding. The male and female sexual organs are reduced to groups 

 of cells producing either spermatozoa or ova, which usually arise in 



FIG. btf.- 



enlnss Ae, avicularia ; (>,, 

 oesophagus; urz, Ovicells. 



* Ed. Olapar^de, " Beitrage znr Anatomic und Entwickelungsgeschichte (ier 

 Seebryo/.oeu." Zeit.f. miss. ZooL. Tom. XXL, 1871. 



