OBSERVATIONS OX FJiESH-WATER POLYZOA. 



123 



the colony that is to grow. At the same time they must be looked 

 upon as assisting- (listril)ution to a great extent. B}^ their means, 

 foT instance, the statohhists have a chance of clinging to the feathers of 

 some water-birds or to floatmg logs or weeds and of being carried away 

 to distant localities. The strongly developed hooks on tlie statoblasts 

 of Cristntdla or of Pect, magnißca, in which the annulas is but 

 weaklv developed and cannot serve more than as a mere buoy, may 

 perhaps have in this respect a great importance. In the present 

 species, the extreme insignificance of the hooks as distributing organs is 

 probably sufficiently counterbalanced by the extensively developed an- 

 nuhis with its double curvature, so marked a feature of this as compared 

 with all other species. Braem regards the hooks as protective organs, 

 but as such they can have no great value in the cnse of Feci, fiel atinosa. 



The annul us, as studied on sections (fig. 46, PI. XIX), is made 

 up as usual of two h(^rizontal strata, each consisting of a single 

 layer of upright hollow prisms which -remind us of cells in a honey- 

 comb. The central part shov^dng indistinct reticulation in sur- 

 face-yiews proves to be the exposed surface of a thick chitinous 

 capsule of spheroidal shape (centr. caps.^ This central capsule is 

 made up of two watch-glass like valves tightly apposed with rims, 

 the demarcation between them being visible as a faint line. The 

 wall is composed of two distinct layers of chitin, which maybe called 

 the outer and the inner stratum respectively. The outer is darker 

 in color, and by far the thinner of the two. This stratum is the 

 continuation of the chitinous wall of the annulas, and its exposed 

 surface is raised into l<nv ridges that form a network with hexagonal 

 meshes. 



The thick inner stratum of the chitinous capsule looks bright 

 yellow on sections. Directly beneath this capsule, there is a mem- 

 branous envelope (r//ü. /^?^'//;/;y.) distinctly composed of flat hexagonal 



