ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 773 



be independent of the principal apparatus, and seems to act under 

 special conditions. 



In the Cercopidae, whose wings present at the base of the anterior 

 margin a triangular enlargement, the external side of the triangle 

 is armed with a row of hooks, few, but very strong, whose extremities, 

 sharply bent, are directed backwards. These hooks are also seen in 

 the Tettigoniidte and in Ledra where they are very small. 



In some Membracidaa there are vestiges of these hooks in the shape 

 of long straight hairs, inclined backwards. It is important to note 

 that in Ihelia expansa, which has only two or three of these hairs, 

 they occupy the widened region of the edge of the wing. 



In Cicada and Fulgora, the principal connecting apparatus is con- 

 tinued as far as the base of the wing by a sort of marginal nervure, 

 forming a very strongly marked rim. 



Many of the Henri ptera fly but rarely ; the flight of the Hymen- 

 optera, more powerful and better directed, is therefore much more 

 sustained, and from this comparison most naturalists seem to conclude 

 that the organs of flight in the latter exhibit the highest degree of 

 perfection. The author thinks, however, on the contrary, that the 

 double function of the hemielytra, which serve at the same time both 

 as wings and for sheaths, involves special complication in the form of 

 the organs of flight. 



P- Myriapoda. 



Diversity of Type in Ancient Myriapods.* — S. H. Scudder dis- 

 cusses the systematic position of Palwocampa (Meek and Worthen), 

 and comes to the conclusion that it is neither the caterpillar of a 

 lepidopterous insect nor a worm, but a myriapod of a new and strange 

 type. 



This brings us face to face with two remarkable facts : First, that 

 in this ancient myriapod, carrying us back as far as any traces of 

 wingless tracheate arthropods have been found, and therefore presum- 

 ably not far from the origin of this form of life upon the earth, we 

 find dermal appendages of an extraordinarily high organization, more 

 complicated than anything found in living arthropods, excepting the 

 more varied scales of several orders of hexapods ; a form of appendage 

 which it would seem, on any genetic theory of development, must 

 have required a vast time to produce, but which we now seem to find 

 at the very threshold of the apparition of this type of arthropod life. 

 Second, that at this early period, in marked contrast to what we find 

 in other groups of articulated animals, the divergency of structure 

 among myriapods was as great as it is to-day. The structural rela- 

 tions of myriapods and hexapods render it probable that the former 

 preceded the latter ; and in complete accordance with this expectation, 

 the structural relations of the oldest fossil myriapods indicate their 

 apparition at a period earlier than that to which the winged insects 

 are hypothetically assigned. This would compel us to consider the 

 earlier typo as aquatic, for which we have presumptive evidence in 



* Amer. Journ, Sci., xxiv. (1882) pp. 161-70. 



