48 



BRYOZOA ECTOPROCTA. 



develop further, they become more distinctly marked off from one another 

 (Fig. 23 B), and finally shift quite apart, a portion of the tissue of the neck 

 of the hud being used for the development of the adjacent parts of the zooecial 

 wall (Braem). Xitsche had already observed this form of origin of one 

 polypide-rudiment from another, and defined sucli forms as double buds. In 

 Pliimatella, as veil as in Cristatdla, the first bud to develop in each polypide 

 {B, C in the diagram, Fig. 21) forms after the type of the double bud. The 

 buds that develop later {B\ B^, C'\ etc., in the diagram) form after another 

 type which, however, is not essentially different. The rudiment of the bud 

 here arises (Fig. 23 C, h) in the zooecial wall itself on the oral side of the parent 

 ))olypide-rudiment ; the young bud-rudiment is, however, from the first, in 

 direct connection with the germinating tissue of the parent-rudiment, so that 

 here also Ave can recognise the connection of each new rudiment with an older 

 one. "We can see here very clearly that budding is to be traced back to a 

 process of division. Each newly arising individual becomes cut off from an 

 older individual already present, so that finally all the individuals of a colony 

 can be derived from the first individual produced from the larva. 



a 



Fio. 24.— Biuldiiii; in Palvdicella Ehreniergii (after Davenport). Median section through the 

 fjrowing apex of a branch, a, b, region of the branch belonging to most distal of the 

 polypides as yet developed ; h, c, region belonging to the polypide-bud (p) that is beginning 

 to develop ; c, d, region of the growing tissue at the tip of the branch ; d, growing tissue ; 

 ed, hind-gut of the polypide ; g, ganglion ; p, young polypide-bud. 



Authors still differ as to the development of the zooecial wall in the Phylacto- 

 laemata. Brap:m is inclined to derive it exclusively from the germ-tissue of the 

 neck of the bud, but Davenport maintains that the zooecial wall grows 

 independently in Cristatella, at least at the marginal parts of the colony. 



Another method of budding, in which the rudiment of the polypide has 

 from the first a certain independence, forms the transition to the type of 

 budding in which the zooecium develops first, a type common in the Gynino- 

 laemata. Fig. 24 illustrates the rise of new individuals at the apex of a 

 branch of raludicella (Davenport). The apex of the branch is here occupied 

 by actively growing tissue {d), which gives rise.first of all to the zooecium of the 

 new individual. While the wall of this new zooecium undergoes the general 

 histological transformation by means of which it attains the special character of 

 the adult form, the tissue, at one definite point, retains its embryonic character 



