On a Parasitic 8i)onge. By Prof. P. Martin Duncan. 379 



270 diameters — resolves, under transmitted liglit, the thin mem- 

 brane of the whole into very definite histological elements. 



1. A series of external cells, circular in outline, large, in contact 

 at their edges and thin (t igs. 4, 5, 7). 



2. Minute circular spots, one on each cell centrally, which 

 permit light to pass through them more readily than through the 

 surrounding tissue (Figs. 4, 5, 7, 8). 



3. Spinules which project at right angles from the sacs, tubes, 

 and chambers ; they are transparent, rather blunt at the tip and 

 broad at the base, usually straight and cylindro-conical, but some- 

 times they are bent and rather deformed. They spring from a 

 dark base with sometimes a central luminous spot, and their bases 

 are modifications of the cellular element (No, 1). They are more 

 numerous and longer in some places than in others, and are 

 crowded on some parts of the parent sac, and are sparely yet 

 decidedly distributed on the stolons and smaller chambers (Figs. 

 1,2,3,4,6). 



4. Minute spinules, which resemble the larger in their shape, 

 and are outward continuations of the cell-membrane around the 

 luminous spots (Fig. 6). 



5. A deep layer of cells is evident ; but they are very thin, and 

 resemble those on the surface. 



6. In some parts, the spinules and luminous spots tend to form 

 groups and irregular patterns (Fig. 2). 



7. No fibres are to be distinguished, and no canals permeate 

 the thin membrane. This is porous, and a side view indicates that 

 the continuity of the outside tissue is imperfect at the luminous 

 points and between the edges of the circular cells. 



Doiiht/ul Histological Elements. — A very delicate refracting 

 fibre is seen adhering to the under part of the parent sac, and in 

 another part there is a glassy-looking acicular spicule in the same 

 position. But careful focussing shows that neither enter into the 

 composition of the organism, and that they are simply adherent 

 and probably foreign to it. Nevertliclcss they are of importance 

 in relation to similar structures which arc seen in other siiocimens. 



The higher magnifying power distinguishes some small open- 

 ings, with relics of stolons attached to them, on the parent sac, in 

 one of the smaller chambers and on one of the stolons, and it casts 

 some doubt upon the entry of a stolon into a largo sac at the side 

 of the forumiiiiferal chamber. Very probably — for unforlunately 

 the thickness of the section and glass cover ])rcvcnts certainty — there 

 are two of these organisms close together, both having conununicii- 

 tion with a neighbouring foramiuiferal chamber through the 

 nummuline wall. 



Under polarized light, the whole of the organism gave faint yet 

 decided indications ol' doiililo refraction, in and about a host of 



2 c 2 



