INTRODUCTION. Clll 



Smitt has raised an interesting question as to the 

 precise nature of the buds which are developed from the 

 margin of the zoarium, and give rise to the new lines of 

 cells. Round the growing edge of the colony, in the 

 incrusting forms, we find a membranous or subcalcareous 

 expansion, which is divided by slightly raised lines into 

 numerous areas (see Plate XXIX. fig. 3). On these par- 

 tition-lines, as foundations, the side- walls of the new cells 

 are ultimately built up. This expansion Smitt considers 

 to be a colonial growth — a common bud {" samknopp ") , 

 which divides, and is developed into separate cells'^. 

 But the interpretation seems to me both antecedently 

 more probable and more in harmony with the facts of the 

 case, which regards each of the marginal areas, ultimately 

 developed into cells, as derived from an individual zo- 

 oeciumf. The inclosed area is often of considerable 

 length, and may divide transversely into several cells, or 

 (sometimes) longitudinally into two ; but in all cases it 

 seems probable that it is in its origin a growth out of 

 one of the older elements of the colony, not a mere "seg- 

 ment of a common bud J. 



The mode in which the calcareous ectocyst or outer 

 wall of the zocecium is formed is a point which has 

 received less attention than it deserves. In many species 



pp. 5-16 : Claparede, Zeitsch. &c., xxi. : Nitsche, Zeitscb. xxi. 1871, Heft 4, 

 p. 58; "JJeh. die Knospung, Y. Loxosoma," Zeitsch. xxv. Suppl.-B. Heft 3, 

 p. 146 : Hatschek, " Knospung der Vedicellina echinata," Zeitsch. xxix. (1877) 

 p. 517 : Metschnikoff, Bull, de I'Acad. de St. Petersbourg, xv. (1871) p. 507 : 

 Ehlers, 'Hypophorella,' p. 77 : Vogt, On Loxosoma, Arch, de Zool. experi- 

 mentale, 1877 : Saleusky, " Etudes sur les Bryozoaires Entoproctes," Ann. 

 d. Sc. Nat. 6'^ 861-. Zool. v. (1877) ; Zeitsch. xxii. pp. 343-348. 



* " Om Hafsbryozoernas Utveckling," CEfv. kongl. Vet.-Akad. Forh. 1865, 

 no. 1, p. 6. 



t See Nitsche, Zeitschrift, &c., xxi. 4 Heft, p. 66. 



\ At page 223 a different mode of gemmation is described, wliich occurs iu 

 some of the Cheilostomatous species. 



