ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 971 



basis of those now persisting. (3) The Hemiptera, Ortlwptera proper, 

 Plecoptera, Ephemeridse, Libellulidee, and Neuroptera proper, are repre- 

 sented in Palaeozoic times. The representation is confined, however, 

 to specific groups, to the Cicadas among Hemiptera, Hemerobidse 

 among Neuroptera, Phasmidse and Blattidse among Orthoptera, by 

 dragon-flies among Libellulidse. (4) The Palaeozoic forms do not throw 

 any clear light on the origin of other insect orders with complete 

 metamorphosis, nor on the transitional links and synthetic types 

 which connect those already mentioned. (5) Brauer believes that 

 the beetles do not form a transition type from Neuropteran or other 

 Palaeozoic insects to the subsequent metabolic forms, but that they 

 represent the end of a typical developmental line, and further, that 

 the division into insects with complete, and insects with incomplete 

 metamorphosis is unnatural. (6) No proof can be advanced in favour 

 of the Palseo-dictijoptera of Scudder, or the Neurorthoptera of Brog- 

 niart. But if the old seven orders of insects be not adhered to, the 

 name Neurorthoptera may be well applied to the modern Plecoptera, 

 and Neuroptera restricted to Libellulidee and Epliemeridse. (7) Erich- 

 son's proposal to unite his Pseudo-neuroptera in one order, and that 

 with the true Neuroptera is quite unnatural and impossible. 



Contagious Diseases of Insects.*— Mr. S. A. Forbes gives a 

 detailed account of his observations and experiments on the contagious 

 diseases of certain insects. The ravages of the European cabbage- 

 worm (Pieris rapse) are checked by their liability to a common 

 disease, marked by the whitening of the living larvae and their rapid 

 post-mortem blackening. The circulating fluids are white and 

 opaque, laden with spherical granules, 5-7 p in diameter ; the mucous 

 membrane of the chylific stomach degenerates ; the alimentary fluids 

 and blood exhibit unmistakable micrococci ; the fatty bodies undergo 

 immense degeneration. 



That the disease is contagious is shown by its unequal distri- 

 bution in a neighbourhood ; by its gradual though rapid progress 

 through a field ; by its independence of locality, climate, and weather ; 

 by its apparent progress across a country from east to west ; by the 

 probable success of infection ; and, finally, by its evident bacterial 

 character. 



An account is given of numerous cultures and their results, 

 but no opportunity offered for infecting a healthy larva with the 

 microbes. 



A more complete study was made of the jaundice disease of the 

 silkworm, which is marked by the yellow colour and restless activity 

 of the larvas, by the tender skin and free flow of blood, and by the 

 crowding of the blood with the results of tissue degeneration, chiefly 

 of the fatty bodies and blood-corpuscles. 



The disease is essentially a premature pupal histolysis of the 

 fatty bodies, or a retardation of pupation which takes unequal effect 

 on the different tissues. This supposed jaundice is also contagious, 

 as was shown from the phenomena of its occurrence ; and the 



* Bull. Illinois State Laborat. Nat. Hist., ii. (18S6) pp. 257-321 (1 pi.). 



