380 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the fifth generation developed therefrom is bisexual ; from the fertilized 

 egg the animal which is to live over the winter is slowly developed, and 

 it gives rise to the first generation of the cycle. Further details are 

 given as to other species of the genus. 



The developmental history of Phylloxera is also incompletely known 

 and is more complicated than is generally supposed ; in many points 

 there is a resemblance to what obtains in Chermes, and it is probable that 

 forms which are generally regarded as specifically distinct belong to 

 different periods in one developmental cycle. There are, also, reasons 

 for supposing that external conditions may affect the rotation in which 

 the various stages follow one another. In P. coccinea there are two and 

 not only one winged sexupara during the year, for there is one at the end 

 of June and another at the end of August ; in addition to the wingless 

 sexupara of September, described by Balbiani, there are others in July 

 which produce a number of males or females. The author has brought 

 together numerous facts relating to the life-history of these insects, and 

 concludes that, in the natural development of Phylloxera vastatrix, the 

 gall-generation never follows directly on the parthenogenetic root- 

 generation ; the first young form (stem-mother) which arises from the 

 fertilized winter egg and its direct descendents, sometimes for several 

 generations, begins the cycle with the formation of galls. 



Dr. Dreyfus has also published a small treatise * on these insects 

 which may be considered as a monograph of the group. He regards the 

 Phylloxerina as forming the intermediate stage between the Coccinge 

 and Aphidinse, and as constituting a distinct family of the suborder 

 Phytophthires. The group is pretty widely distributed; the most 

 important fact in their developmental history is that, in certain genera- 

 tions, the ova of one and the same mother give rise to completely 

 different animals which pass, simultaneously, through quite different 

 courses of development ; there is, in other words, a division of the 

 developmental series. The author thinks that these " parallel series " 

 will be found in other Insects, and that a knowledge of them will afford 

 the key to the difficulties now associated with their developmental history. 



Chermes.f — Herr N. Cholodkovsky has two communications on this 

 insect, in the second of which he points out how his observations control 

 those of Blocliman and Dreyfus ; he finds that the yellow males and 

 females described by the former do not belong to the developmental 

 cycle of Chermes strobilohius but to that of C. viridis, while the black 

 sexual animals which he has himself found are those of 0. strohilohius. 

 There are similar criticisms of other points of detail into which we 

 cannot enter here. 



S. Araclmida. 



Ecdysis of Spiders.| — M. W. Wagner has made a close study of the 

 phenomena of ecdysis in Spiders. He considers that the casting of the 

 old integument only forms part of the process, and that a secondary one. 

 Some of the phenomena begin at a comparatively long period antecedent 

 to the casting of the skin, and these are partly due to the fact that for a 

 time the animal is deprived of some of its faculties — of sight, hearing, 

 touch, movement, and, for a short time, of respiration. Some of the 



* ' Ueber Pbylloxerinen,' 8vo, Wiesbaden, 1889, 88 pp. 

 t Zool, Aiizeig., xii. (1889) pp. 60-4, 218-23. 

 X Ann. Sc'i. Nat., vi. (18S8) pp. 281-393 (4 jU). 



