8 H. J. HANSEN. 



forth by Latzel ou Scut, immaculata in Austria. This varia- 

 tion in size is connected with differences in certain parts 

 presenting specific cliaracters, and two striking examples 

 maybe pointed out here. In very large specimens of Scut, 

 immaculata the cerci are about six times, whereas in a small 

 specimen they were only four times longer than deep, thus 

 considerably more slender in large than in small individuals. 

 In large specimens of Scut, angulosa^n. sp., the last pair of 

 legs — and to a little lesser degree the penultimate pair, and 

 to a somewhat lesser degree the antepenultimate pair — are 

 more robust and widened, especially in the proximal portion 

 of their tarsi (PI. 4, fig. 2 e) in a way which at least very 

 rarely is met with in small specimens (comp. PI. 4, fig. 2 h, 

 with fig. 3 e, and the explanation of the plate). A similar 

 difference has been observed between the shape of the pos- 

 terior pairs of legs in a large and in a small specimen of Scut, 

 capensis, while in several other species no such difference 

 has been found. Such variation in structural features, gener- 

 ally but not even always proportionate to the size of the 

 specimens, can be very perplexing, and in some cases it is very 

 difficult or perhaps impossible to distinguish with absolute 

 certainty between variety and species without having a rich 

 and well-preserved material from many localities. The genus 

 Scutigerella has caused me much trouble, and I may advise 

 future students not to establish new species without a very 

 careful and prolonged examination of several forms, and 

 never to establish a species on specimens not having acquired 

 the full number of legs, or on specimens in which the legs of 

 the twelfth pair are not quite as long and do not possess so 

 many set^e as those of the eleventh pair. 



B. Head. — It is comparatively shorter and broader (and 

 thicker) in Scutigerella than in Scolopendrella, but the pro- 

 portions between the dimensions in question vary conspicu- 

 ously between the species of the same genus. While the 

 breadth is easy to measure when the animals are seen from 

 above, the length can often only be measured with accuracy 

 when they arc seen from the side ; I have often not found it 



