NOTES AND MEMORANDA. 293 



is proved that excitation of this nerve quickens the pulsations of the 

 heart and augments their energy, while section of it slows the heart. 

 Excitation of the thoracic ganglia always retards the heart, the con- 

 verse of the cardiac nerve. Acetic acid applied to the heart substance 

 arouses its contractions even when they have ceased, and maintains 

 them for several hours. 



The action of a number of other substances is equally noteworthy, 

 and M. Plateau's full communications to the Academie Eoyale of 

 Belgium will be awaited with interest by physiologists.* 



Natural Classification of the Spiders. — Dr. Bertkau points out f 

 the great difficulty of classifying the group ; comparing them with the 

 Insecta (Hexapoda), he says that the body is only divided into two 

 regions, that there are no antennae or wings to aid in discrimination, 

 and that even those parts, which vary in other Arthropoda, present iu 

 tbera a remarkable uniformity ; thus there are almost always eight 

 eyes, and a variation in the number of these is of doubtful value, the 

 mouth-organs are always of the same structure, and the number of 

 joints in the legs is very fairly constant ; nor do the spinning warts 

 afford any greater aid. Turning to the variations in their habits, he 

 observes that Aristotle, just as much as the latest systematists, drew 

 attention to the difference in the characters of the web, and of the 

 methods by which these creatures obtain their prey, but these differ- 

 ences are of no value as aids to classification from a morphological 

 point of view. 



In the present essay an attempt is made to take into account all 

 the variations in organization, and to use only the characters of the 

 web as a last resource, for the very excellent reason that these are of 

 no assistance in the classification of dead Spiders. The following is a 

 short outline of the grouping here proposed : — 



Sub-order I. — Tetrasticta ; two pairs of stigmata on the lower 

 surface of the abdomen ; ovaries and testes circular, the entrance to 

 the seminal pouches simple, and just in front of the orifice of the 

 oviduct. 



i. Atypidce ; with eight eyes, all four stigmata leading to the 

 "lungs"; six spinning warts, the anterior pair short, and consisting of 

 one joint ; mandibles horizontal in direction ; more than one recepta- 

 culum seminis. 



ii. Di/sderidcB ; with six eyes, the two hinder stigmata leading 

 into a tracheal system ; the six spinning warts sub-equal, and all 

 consisting of one joint each ; mandibles vertical, or directed obliquely 

 forwards ; only one receptaculum seminis. 



II. Trisdcta. — Only one pair of stigmata on the lower surface of 

 the abdomen ; ovaries and testes in two branches ; there are ordinarily 

 two openings into the seminal pouches. 



These are divided into nineteen families, many of which have 

 well-known names, though their limits are in most cases revised ; 

 their relations to one another are exhibited in a genealogical tree. 



The author considers that the Tetrasticta are the more primitive 



* ' Nature,' xix. (1879) 470. 



t ' Arch, fiir Naturgeechichte,' xUt. (1878) 351. 



