HIRCINIA. 177 



millim., aud end with a terminal pyriform swelling 0*006-0'01 millim. thick — 

 the terminal knot. F. E. Schulze has studied the filaments o£ this species 

 very carefully. They consist of an axial thread, surrounded by a pith-like 

 substance, which forms the biUk of the structure. The outermost layer is very 

 hard and resisting, and forms a kind of cuticle on the surface of this pith- 

 cylinder. In the terminal knots concentric layers are observed in the super- 

 ficial part, and often large granules in the interior. Occasionally similar knots 

 are situated in the course of the fibre, and then it may happen that three or 

 four fine threads issue from one such knot. The amount of nitrogen in 

 the filaments has been calculated by Maly at 9*2 per cent., whilst the percentage 

 of nitrogen in the spongin-fibres is over 16 per cent. The filaments are 

 generally more abundant on the surface than in the interior. 



The inhalant pores are pretty uniformly scattered over the surface. They are 

 about 0*01 millim. wide, and lead into special perpendicular canals of similar 

 dimensions, which penetrate the skin and open into the subdermal cavities, 

 0'l-0-3 miUim. wide, which undermine the skin. These appear as anastomosing, 

 irregular tangential, radially compressed canals with an oval transverse 

 section. The inhalant canal-stems proper, which arise from the floor of this 

 subdermal cavity, are on an average only 0"1 millim. wide, and show very 

 marked annular strictures. The ciliated chambers are 0*04 millim. wide, pyri- 

 form, and provided with very short special efferent canals. The afferent pores 

 leading from the final ramifications of the inhalant system into the chambers 

 are small. There appear to be several afferent pores to each chamber. The 

 ova and developing embryos are surrounded by special capsules, compared by 

 Schulze to membrance pro]iria'. The collar-cells are confined to the aboral 

 portion of the chamber. Most of the specimens examined by F. E. Schulze 

 were females. In one, however, he observed sperm-balls besides ova. He 

 assumes therefore that in this species not male and female, but hermaphro- 

 ditic and female individuals can be distinguished. In a superficial layer, 

 2 millim. thick, abundant dark brown spherical structures O'Ol mUlim. in size have 

 been observed by F. E. Schulze, which he regards as parasitic Algse. He has 

 observed stages of fission, but no further development. These structures are 

 probably not so much parasitic as symbiotic. They were regarded by KoUi- 

 ker and Polejaeff as young stages of the filaments — not so, however, by F. E. 

 Schulze. 



I distinguish eight varieties of this species for the reception of a niunber of 

 species described by 0. Schmidt and other forms. These varieties are by no 

 means well defined, but appear as sections in the continuous series of changing 

 forms met with in this species. In choosing the limits of the sections of these 

 series to be distinguished as varieties, I have adhered to F. E. Schulze's views. 



