ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 631 



the Orthoptera ; as to the latter point, much supporting evidence is 

 aiforded by the tracheae. The same is true of the bee, for the embryo 

 passes through a stage which recalls that of Macldlis and Campodea, and 

 then becomes very like that of the LejiismidaB. The author considers 

 that the formation of the apodemes must have been cotemporaneous 

 with that of trachete, for both start as infoldings of the hypodermis. 

 When this infolding is filled entirely, or almost entirely, with cuticle 

 (chitin) secreted by the invaginated hypodermis, we have an apodeme, 

 but when the cuticle only invests its free surface, we have a small canal 

 lined with cuticle, that is to say, a trachea with its stigma. Further, 

 there must be a very close connection between the formation of apodemes 

 and of the tracheal system from the physiological point of view, for the 

 thickening of the cuticle requires the formation of new respiratory 

 organs ; the thickening of the cuticle allows the musculature to develope 

 itself more largely, and the musculature, in its turn, tends to produce 

 depressions of the hypodermis, and of the cuticle to which it may become 

 attached ; it tends, in fact, to give rise to apodemes. 



The nervous system and sensory organs are next discussed; this 

 system and the eye of the Thysanura are of the same type as those of 

 other insects, but are comparatively more simj)le. The nervous system 

 of Campodea is still closely connected with the hypodermis, and at 

 certain points (where the ganglia attain their maximum size) it is 

 altogether connected with it, there being no dividing gangliolemma ; in 

 Japijx and others this gangliolemma consists of a simple layer of flattened 

 cells, and in Japyx there is a comjjaratively large lacuna between the 

 gangliolemma and each ganglion. 



The intestine becomes more complicated as we pass from Campodea 

 to Lepisma, the latter resembling the true Orthoptera by its well- 

 developed gizzard, the cui-ves of the median and posterior intestine, the 

 diverticula of the rectum and the salivary apparatus. Prof. Grassi 

 believes that the Malpighian tubules are homodynamous with the 

 stigmata and corresponding tracheae. 



The dorsal vessel is exactly like that of other Insects; no alar 

 muscles wei'e discovered in any of the Thysanura, though they are 

 known to exist in the Collembola. In several, and particularly in 

 Macliilis, there are occasional traces of a vessel uniting the dorsal vessel 

 with the intestine. Anatomical and embryological facts seem to establish 

 the homology of the dorsal vessel of Insects with that of Annelids. 



The Thysanura have, as a rule, an oviduct (uterus), a vagina, and a 

 bursa copulatrix. The first is absent in Campodea only; Machilis has 

 no bursa and appears to be simpler than its allies. The arrangement 

 which obtains seem to support the views of Palmen as to the double 

 nature of the genital ducts. 



After a somewhat detailed account of the generative apparatus the 

 author concludes that in the ancestors of Arthropods the sexual products 

 were, as in certain Annelids, eliminated by means of the segmental 

 organs ; later on one of the two pairs was closed ; in the secondary 

 sexual organ of Campodea there exist signs of the closed pair. 



The appendages, especially the gnathites, are discussed at some 

 length ; all the Thysanura have a galea (external lobe of maxilla) ; this 

 is a character which is repeated only by the Orthoptera and some 

 Neuroptera, and is not found in any other insect. 



Passing to systematic problems Prof. Grassi asks if the order of 

 the Thysanura is a natural one. He thinks it is, and he places it under 



