ZOOLOGY AND BOTANY, MICK08C0PY, ETO. 635 



the ventral surface has been from the first indicated by the position 

 of the mouth. The acquisition of a direct motion occurs some time 

 after the animal is truly bilateral, an indirect revolutionary motion 

 being gradually changed into a direct motion with its anterior ex- 

 tremity in advance. 



Symbiosis of Bryozoa and Actiniae.* — W. A. Haswell dredged 

 specimens of a branching species of Cellepora, which was dotted 

 over with small red specks, and on examining these more minutely, 

 he found each to consist of a minute Actinid lodged in a cylindrical 

 pit excavated in the substance of the polyzoarium, and projecting, 

 when expanded, about a quarter of an inch from the surface of 

 the latter. Each of the pores was about l-20th in. in diameter ; 

 tbey are cylindrical and tolerably smooth, and in most cases the 

 orifices are furnished with a low projecting rim. When they 

 are traced backwards into the substance of the Cellepora, two are 

 frequently found to unite, and very often they eventually open into 

 the cavity occupying the centre of the thicker branches. They very 

 often extend in this way through a distance many times greater than 

 the length of the Actinid itself, and as the latter is provided with no 

 means by which it can retract itself into the interior, this long canal 

 must be the result of the simultaneous growth of the little anemone 

 and the Cellepora in which it is lodged. 



This singular phenomenon is specially interesting, on account of 

 the light which it throws on the structure of some very problematical- 

 looking species of Bryozoa, one of which Mr. Haswell recently de- 

 scribed as Sphceropora fossa {Cellepora fossa). In this species the 

 bryozoarium is spherical, slightly compressed, one pole being always 

 characterized by the presence of the deep cylindrical pore running in 

 the direction of the axis, but not quite reaching to the opposite pole. 

 This pit is always well defined and uniformly cylindrical, and it is 

 difficult to explain its nature unless we suppose that it was occupied 

 by a minute Actinid similar to those already described. None of the 

 specimens seen exceeded l-8th in. in diameter, and most of them, 

 from their worn appearance, must have been dead when dredged, so 

 that there would seem to be a tendency in this species to arrest of 

 growth and death at a certain definite stage of growth. This species, 

 it is to be remarked, differs entirely in the nature of its zooecia from 

 the branching species already mentioned, which is a normal Cellepora. 



A species very nearly related in the peculiar form of the cells to 

 C. fossa was dredged off Port Stephens. The form of the bryozoarium 

 in this case is usually that of an elongated cone, l-3rd in. to 1-2 in. in 

 length, with a pit exactly like that occurring in C. fossa, in the centre 

 of the base ; but sometimes it has the form of a circular plano-convex 

 disk l-3rd in. in diameter, with cells on both sides and without a pit, 

 while in other cases the shape is more irregular, subhemi spherical or 

 the like, but never larger than a pea. 



It seems very likely that the first-mentioned species starts from an 

 early stage, resembling C. fossa or its ally, a group of cells surround- 



* Proc. Linn. Soc. N. S. Wales, vii. (1883) pp. 608-10. 



