30 T. THORELL, 
them sufficient weight, when we set up for the forms which exhibit them, 
within the family Zpeiroide the sub-family Uloborine, and within the family 
Agalenoide the sub-family Amaurobiinæ, and moreover among the Saltigrade 
reckon the Æresoidæ and Dinopoide as separate families, — they cannot 
be allowed the importance which BLACKWALL ascribes to them. In the first 
place it is very uncertain, that the organ, which BLACKWALL considers as 
a pair of spimers grown together, really is so; I for my part do not think 
so, for it does not project above the surface of the abdomen, but seems 
only to consist of a peculiarly modified part of the skin, neither have I 
been able to discover any spinning-tubes on its surface 1). But even if 
BLACKWALL'S explanation of that organ is right, still the family Mygalide 
BLACKW. proves, that the number of spinners needs not be the same in all 
the genera belonging to one and the same family; for to that family BLACK- 
WALL himself reckons genera not only with four but also with six spinners. 
As regards the calamistrum, the purpose of that apparatus in the animal’s 
economy is perhaps as yet too little known to justify the laying of any 
great weight upon it in classification. If DLACKWALL'S statement, that it is 
a curling-apparatus used in the construction of the spiders web, ?) is cor- 
rect as regards the genera Amaurobius and Dictyna, which I have no rea- 
son to doubt, it can hardly have the same functions in, for ex., the species 
of Uloborus and Hyptiotes (Mithras), which weave regular, so-called geo- 
1) It is a matter deserving of investigation, whether the infra-mamillary organ be 
not connected with trachee, having their stigmata in or close to that organ. That 
some spiders (Dysderoide, Argyroneta) have two tracheal trunks opening on the 
ventral surface of the abdomen, near its base, behind the openings of the two so- 
called pulmonary sacs, is generally known. In some other species MENGE (Ueb. d. 
Lebensweise d. Arachn., p. 23; Preuss. Spinnen, p. 81, 189 ete.) has discovered a 
system of tracheæ opening at the end of the abdomen, immediately in front of the 
spinners, with either two stigmata (certain Attoide and the Erigone- and Walcke- 
naera- or Micryphantes-species) or only one (Cercidia or Cerceis prominens). But 
according to v. SIEBOLD (Vergl. Anatom., p. 535) there is in most spiders — he 
reckons up the different genera Æpeira, Tetragnatha, Theridion, Drassus, Clubiona, 
Lycosa, Dolomedes, Thomisus (Xysticus) — a fissure before the spinners, from 
which proceed four flattened, band-formed, almost always unramified tracheæ. It 
seems then that a tracheal system is to be found in all spiders provided with only 
two "pulmonary" sacs, although it may terminate sometimes with one and sometimes 
with two very variously situated apertures, and it is certainly not wanting in those 
genera, which have an infra-mamillary organ and calamistrum. 
2) As to BLCKwALL'S beautiful and highly interesting researches on this subject, 
vid. Buackw., Notice of sev. ree. discov. in the struct. and ceconomy of spiders, p. 
472 et sequ. 
