ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 31 



Pupal Histolysis in Diptera.* — C. Vauey has studied this in arti- 

 ficially reared larvas of Gaslrophilus cqui and in species of Chironomus, 

 and gives an account of the various stages in the process. In CEstridae, 

 as in Muscidre, the destruction of the tissues is duo to phagocytes, which 

 are no other than the cellular elements of the blood. Iu the blood of 

 Chironomus, however, there are no elements which can act thus, and the 

 phagocytosis is due to individualised cells of the adipose tissue. 



Role of "Phagocytes" in Insect Metabolism.f — Prof. Antonio 

 Berlese publishes a brief note on this subject. He considers that the 

 term phagocyte is totally inapplicable to the amcebocytes or leucocytes 

 of larval insects ; for not only have these no destructive action on the 

 larval tissues, but also they are incapable of digesting the detritus when 

 these tissues have broken down. Their function is twofold : — they serve 

 to transport elaborated food-material to areas in which formative pro- 

 cesses are going on, and they are also capable of giving rise to new 

 mesodermal tissue by direct transformation into its elements. Elements 

 of the fatty body in the newly-hatched larva, and muscular elements, may 

 arise in this way from leucocytes. When these convey food-material, 

 they do not alter it in any way, so can have no digestive properties. 

 In general they may be said to be the exact opposite of phagocytes. 



Histolysis in Muscidse.t — Prof. F. Henneguy agrees with Berlese 

 that the cells of the fatty body (in Calliphora vomitoria and Lucilia 

 csesar) are never attacked by phagocytes. As Berlese says, these cells 

 are trophocytes, — elements which elaborate the substances necessary for 

 the nutrition of the tissues of the nymph. Henneguy does not, however, 

 deny that it may be otherwise ; e.g. as Vaney describes, in (Estridaa. 



Freezing of Body Fluids in Insects.§ — P. Bachmetjew has con- 

 tinued his observations on the " critical point " in insects cooled below 

 freezing-point. His previous results showed that, as is the case with 

 water in capillary tubes, the body-fluids can be cooled considerably 

 below their -freezing- point before solidification occurs, and when it does 

 occur there is an instantaneous rise of temperature to the normal freez- 

 ing-point. His present results show that the exact point at which the 

 solidification occurs (the critical point), depends, among other causes, 

 upon the rate of cooling, but this dependence is by no means of a 

 simple kind. Thus, a certain rate of cooling gives the critical point 

 its minimum value in Vanessa atlanta and Papilio podalirius, and its 

 maximum value in Pier is rapse and Aporia cratsegi. Again, the critical 

 temperature differs in different species, though it may perhaps be said 

 generally that the larger the pupa the higher is the critical temperature, 

 i.e. the nearer it is to the freezing-point. The behaviour of para-nitro- 

 toluol and benzol, when subjected to temperatures lower than those of 

 their normal points of solidification, showed a striking analogy to that 

 of the fluids of insects. 



Silk of the Procession-Caterpillar.|] — Prof. B. Dubois notes the 

 interesting fact that this caterpillar — Cnetocampa processionxa — spins 



* Comptes Rendus, cxxxi. (1900) pp. 758-61. 



t Zool. Anzeig., xxiii. (1900) pp. 441-9. 



X Comptes Rendus, cxxxi. (1900) pp. 90S-10. 



§ Zeitschr. wiss. Zool., Ixvii. (1900) pp. 520-50 (3 figs.). 



|| Ann. Soc. Linn. Lyon, xlvi. (1900) pp. 125-7. 



