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ludiinentaiy, Ijointed and have a very short seta, and so they are in the seven remaining 

 species belonging to the group of Sphcer. Leuchartn Sal. (comp. the systematic part). 



The Rostrum. It is always of good size and bluntly conical, or like a cylinder 

 with dilated base. Its structure is very complex, and we will begin by studying its distal 

 part, for the representation of which Choniostoma Hansenii (pi. X, fig. 6a and fig. (Jb) will 

 serve as type. In fig. Ga the cylinder is seen sideways and without the expanded part at 

 its base. At the margin of the terminal face of the cylinder originates a membrane which 

 has the shape of a kind of border or very short inverted cone. In looking at it from the 

 distal end (fig. 6b) we see that the membrane covers the whole tei-minal face, having the 

 shape of a cup or perhaps rather of a flat funnel, as it leaves an oblong aperture at the 

 bottom in the centre; tliis is the entrance of the mouth, beyond the margin of which the 

 points of the mandibles are seen to proceed. In front of the mouth the membrane is divided 

 in the middle by a deep incision; the opening thus produced is filled by an odd median plate, 

 on each side of which is another plate which is partly covered by the membrane. In the 

 illustration these parts are marked d. The membrane is downy at its edge (fig. Gb), and 

 the whole inner surface of the funnel is covered with peculiar dots, which are smaller near 

 the edge than towards the centre, and which probably represent tiny knots. Outside the 

 membrane are seen a number of cylindrical hairs which are sometimes furcate at the apex 

 (b). They are articulated to the distal edge of the cylinder at the base of the membranous 

 border and, being longer than its height, proceed somewhat beyond its li^ee margin. When 

 — as in the present instance — the rostrum is cut off, it is easy enough to see that these 

 hairs do not exist within the membrane, but only lean against it. In some species, e. g. in 

 Sphceronella curtipes (pi. X, fig. 2d), the membrane (viz. the free part of it) is considerably 

 broader, in others narrower, than in Choniostoma Hansenii. The hairs in some species are 

 much more numerous and much thicker than in others, and they often converge or diverge very 

 ii-regularly, according to the position they happen to occupy ; in a few species I was not able 

 to discern them. My figures as a rule are too small to allow of drawing the membrane, but 

 these hairs are drawn as well as it could be done. It must be observed that the shape of 

 the mouth varies considerably in specimens of the same species; I have found it more or less 

 funnel- or cup-shaped, in accordance with the angle formed by the membranous border and 

 the surrounding hairs against the terminal face. In the systematic part of the present work 

 the free part of the membrane together with the hairs is called the mouth-border. 



The outer surface of the rostrum shows several harder chitinous lists, and when the 

 rostrum is examined from its distal end, some harder parts are seen thi'ough the semi-dia- 

 phanous membrane as circles, which are interrupted in front at the median line. In my 

 opinion the distal part of the rostrum nuist be explained as being a liiglily modified Jahium, 

 or rather hypopharynx, which forms a kind ot sheath round the mandibles and stretches so 

 far towards the front that its edges approach very near to each other, and that the above- 

 mentioned median part marked d. must be considered as the hilinim. However, I am not 



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