XVIII 



MOVEMENTS OF COLONY 



497 



After a time the narrow connection breaks, and two new colonies 

 are formed. 



Fig. 248 shows a colony shortly after division has taken place. 

 The colony had moved forwards, in 

 a direction away from its apex, for 

 three days in a nearly straight 

 line, the distances moved in each 

 day being respectively 6, 8 J, 8-g- 

 mm. These observations, for which 

 I am indebted to Mr. Lister, show 

 a considerably higher speed than 

 in those recorded by Trembley, 

 who observed no colony which 

 moved more than half an inch 

 (12*5 mm.) in eight days. 



The genus Pectinatella also has 

 some power of locomotion. This 

 magnificent Polyzoon occurs in 

 masses several feet in length (as 

 much as six feet in P. gelatinosa 

 from Japan l ), and four to eight 

 inches in thickness. The greater 

 part of P. magnified 2 consists of a 

 thick, opaline, and gelatinous ecto- 

 cyst, the upper surface of which is 

 covered by hundreds of rosette-like 

 colonies, which increase in number 

 by division. The masses are thus 

 aggregations of colonies, which 

 secrete a common basal ectocyst. 



Fig. 248. Lophopus crystallinus Pall., 

 Cambridge, showing the rate of 

 movement. The colony and the 

 distances moved are x 2. 



The latter decays in the 

 autumn ; and the separate rosettes, or groups of them, may thus 

 be set free, being found as floating masses, which may again 

 attach themselves to a solid object till the time of their death. 

 Pectinatella has not yet been recorded in England, although, con- 

 sidering the ease with which statoblasts are transported, it is by 

 no means improbable that it will eventually be recorded as a 

 British genus. It is at present known to inhabit America, 

 Japan, and Hamburg. 



It is by no means certain what is the mechanism by which 



1 Oka, J. Coll. Japan, iv. 1891, p. 90. 2 Hyatt, t tit. p. 99. 



VOL. II 2 K 



