HARDWICKE'S SCIENCE-GOSSIP. 



105 



The exact form of these mushroom-bodies is not 

 easy to be made out from preparations such as that 

 figured by Leydig, and, indeed, the appearance pre- 

 sented by sections does not convey a very clear idea 

 of their form. 



In the middle of the primary lobe, as figured by 

 Leydig, there is a rounded mass, which he describes 



Fig. 93.— Diagrammatic outlines of sections of the upper part of the brain of a Cockroach. Only 

 one side of the brain is here represented. The numbers indicate the position in the series 

 of 34 sections into which this brain was cut. mb, mushroom-bodies, with their cellular cover- 

 ing ; c, and their stems, st ; a, anterior nervous mass ; m, median nervous mass. 



as a "giant nucleus " {ma), but more recent researches 

 have shown that Leydig was mistaken, and that this 

 appearance is really the optical section of a cylinder 

 of nervous matter, which passes forwards, to end 

 abruptly upon the front surface of the brain. The 

 structure was correctly described by Dujardin, in 

 1850, but does not seem to have been recognised by 

 Leydig ; this was, no doubt, due to the method of 

 investigation employed by the latter, which consisted 



in clarifying the brain (previously hardened in alcohol) 

 in potash solution, or glycerine. 



With regard to the origin of the nerves of the 

 ocelli (0), it is desirable that Leydig's figure should 

 be verified, for it seems very improbable that they 

 should arise from the heads of the mushroom-bodies 

 in the ant, and from a different part of the brain in 

 other insects.* 



Insects' brains vary very 

 considerably as regards the 

 development of the mush- 

 room-bodies. In ants, bees, 

 and wasps they are propor- 

 tionately large, and double 

 on each side. In the cock- 

 roach they are double, and 

 moderately well developed, 

 and in the mole-cricket there 

 is said to be only one on each 

 side. Dujardin could not 

 detect these mushroom-bodies 

 in the diptera ; but recent in- 

 vestigations (E. Berger, 

 " Untersuchungen iiber den 

 Bau des Gehirns und der 

 Retina der Arthropoden," 

 "Arbeiten des zoolog. In- 

 stituts zu Wien," Bd. i. Heft 

 ii. p. 173) show that certain 

 bodies exist in the blow-fly 

 (Musai vomitoria), and the 

 house-fly {M, domeslica), 

 which, most probably, are 

 correctly regarded as the 

 homologues of mushroom- 

 bodies. 



I had already prepared 

 sections of the heads of several 

 insects, some of which have 

 been exhibited at our meet- 

 ings, before I saw the paper 

 by Dr. Dietl (" Zeitsch. f- 

 wissenschaft. Zool." 1876, 

 vol. xxvii. p. 488), in which 

 some beautiful sections of 

 insect brains are figured and 

 described. When I saw them 

 I determined to try the method 

 he had used for hardening the 

 brains, namely, with hyper - 

 osmic acid. The insect which I selected to work upon 

 was the cockroach (B/aila orientalis). In the first place 

 it was necessary to remove the brain from the head 

 in a perfectly fresh condition, and this required some 

 care, because the organ itself is extremely delicate, 



* I find, since this paper was written, that according to Fli.gel, 

 these nerves pass down beside the mushroom-bodies to 



middle of the "brain. ("Zeitsch. 

 vol. xxx. suppl. p. 556-) 



f. wissenschaft. Zool." 1878, 



