ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 195 



chitinous process. A typical sense-pit shows an opening in the chitin 

 leading down into the pit itself, frequently a channel with spiral folds or 

 various ridges, and a floor produced into the sensory processes which rise 

 like the fingers from a glove. Below the floor is a rounded mass of 

 large radiating cells, each shell separating from its fellow as it approaches 

 the base of the pit and running to its corresponding sensory process. 

 The whole mass of cells is embraced by a branch of the large antennary 

 nerve. In an appendix Prof. H. M. Lefroy suggests that the function 

 of the structures is purely olfactory, that the general surface of the 

 antennae acts for delicate perceptions, that the pits come into play when 

 the concentration of the absorbed liquid has dulled the simple organs on 

 the outer surface, and that the final location of the source of scent is 

 due to the protected pits. Further, it is suggested that the presence of 

 two kinds of pits in some species is correlated with the dual perception 

 in the female of food and of breeding-place ; in the male, of food and of 

 the female. J. A. T. 



Horned Littoral Fly.— L. Mercieu {G. R. Soc. Biol, 1919, 82, 

 1217-18). A specimen of FucelUa ?naritima Hal. showed a minute 

 horn between the eyes, and Yilleneuve suggested that this was due to a 

 hardening and persistence of the frontal vesicle, which is protrusible and 

 contractile on the head of the young flies ; experiments corroborate this. 

 The larvae pupate in the sand under clumps of seaAveed, and some which 

 may find it difficult to get free may 'show a horn. J. A. T. 



Flies in Snails.— D. Keilin {Parasitologij, 1919, 11,430-55,4 pis., 

 6 figs.). The fly Melinda cognata Meigen has its young stages in the 

 small snail Helicella virgata. The oviposition was not observed. The 

 larva occurs first in the kidney, which it destroys, and then in the mantle 

 cavity. It kills the snail and pupates in the earth. There are several 

 hyperparasites of M. cognata, notably two Ichneumonids {Atractodes exilis 

 and Exolgtus petiolarius) which oviposit in Melinda larvae while still in 

 the snail. The early stages of Melinda are described. Three other flies 

 were found in Helicella — viz. (1) another species of Melinda, probably 

 M. geniilis ; (2) Sarcophaga nigriventris ; and (3) another species of 

 SarcoiJhaga, probably >S'. crassimargo. Finally, the author sums up what 

 is known as to parasitic, carnivorous, epizoic, and saprophagous Diptera 

 occurring on living and dead molluscs. J. A. T. 



Photic Orientation in Drone-Fly. — S. 0. Mast {Proc. Amer. Soc. 

 Zool. in A7iat. Record, 1920, 17, 314). It has been maintained that 

 photic orientation depends on the fact that unequal illumination of 

 the two eyes means a difference in the tonus of the muscles of the legs 

 on the two sides of the body. The body, in response to the unequal 

 tonus, is turned until the two eyes are equally illumined. But if the 

 two front legs on one side are removed, orientation is nearly as precise 

 as it is in normal specimens, showing that orientation is not necessarily 

 dependent upon the relation in tonus in the muscles of the legs on 

 opposite sides. If one eye is covered, orientation may still occur. If 

 the two front legs on one side are removed and either eye is covered, 



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