Studies on Bryozoa. 
By 
G. M. RB. Levinsen. 
In a paper: ,,On the Structure and Classification of the .Chei- 
lostomatous Polyzoa"”) Dr. S. Harmer has exposed the chief 
results of his later investigations into the Bryozoa, partly dealing 
with the compensation-sac, first discovered by Jullien, partly with 
the morphology of the front wall, a structure of such great -impor- 
tance in classification. Julliens discovery of the compensation- 
Sac having been either ignored or discredited by later observers, 
Dr. Harmer has so to say, discovered it anew and by new inve- 
stigations into its structure and development supplied Julliens 
short communications. It is a thin-walled membranous sac… lying 
beneath the calcareous front wall and generally opening to the ex- 
terior immediately behind tbe.… proximal border of the operculum 
which is continuous with the hinder wall of the sac. ,,Numerous 
muscles pass from the vertical calcareous walls of the zooecium to 
the floor of the sac. It may safely be concluded that the con- 
traction of these muscles will dilate the sac, thereby introducing 
water into it from the outside and excercising a pressure on the 
fluid of the body cavity resulting in the protrusion of the poly- 
pide." While I quite coincide with Dr. Harmers observations on 
the structure of this sac I do not agree with this author in his 
1) Proceedings of the Cambridge Philos. Soc. Vol. XI, Pt. É pag. 11—17. 
Vidensk, Meddel. fra den naturh. Foren. 1902. 
