42 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and that, during inetakinesis, it divides by fission like the chromo- 

 somes. As to history, it is first observed in one of the early generations 

 of the secondary spermatogonia, and subsequently takes part regularly 

 in the spermatogonial mitoses, differing from other chromosomes chiefly 

 in the possession of a separate vesicle during the prophase. At the end of 

 the spermatogonial divisions it persists as a more or less clearly defined 

 chromosome, at a time when tlic other chromatin elements break up to 

 form the spireme. During the first spermatocyte division it divides 

 with the other chromosomes, but fails to do this in the second division, 

 so that two kinds of spermatozoa are produced in equal numbers. The 

 author believes that those derived from the spermatocyte containing the 

 accessory chromosome possess the power of causing the eggs they 

 fertilise to develop into males, and that thus the accessory chromosome 

 determines sex. 



Histolysis in Metamorphosis of Flies.* — Dr. Paolo Euriques finds 

 that in Calliphora and Sarcoplmga a crystalline substance is formed 

 within many of the larval muscular fibres. This substance finally finds 

 its way into the adipose cells, where it appears in the form of minute 

 crystals. The aggregation of these crystalline bodies produces the ap- 

 pearance described by former authors as endocellular phagocytes. In 

 the sarcolytes engulfed by the phagocytes the striation is lost, and the 

 anisotropic substance segregates to form a large zone, which is luminous 

 when examined with the spectroscojje under crossed nicols. This 

 luminous substance shows successive stages in the development of the 

 crystals mentioned above, and the author believes that these are in all 

 probability derivatives of the anisotropic substance which is taken up 

 by the adipose cells. 



Development of Hypodermal Imaginal Discs in Larval Diptera.f 

 — Dr. Bruno Wahl, as the result of his own observations on Eristalis 

 larvaa, and those of other observers on other flies, finds that in the 

 Diptera generally, the imaginal hypodermis together with its derivatives 

 arises from the larval hypodermis. In the Cycloraphas, the imaginal 

 organs develop from small parts only of the larval organs. Many of 

 the imaginal discs sink below the surface in the form of sacs, and re- 

 main united with the surface only by stalks. In Eristalis this occurs 

 with regard both to the thoracic and the abdominal discs. In both 

 cases the formation of the discs is preceded by histological changes in 

 certain parts of the larval tissues, the cells concerned exhibiting what 

 the author calls " renovation." Its result is to give to the cells a renewed 

 strength and vitality, enabling them to withstand the histolytic influ- 

 ences to which the cells which have not been renewed yield at once. 

 The renewal of the cells of the imaginal discs gives them further the 

 power of regenerating the whole organ of which they themselves 

 originally formed but a part. In other cases, instead of a part only of 

 the cells composing an organ becoming renewed, the whole organ may 

 undergo rejuvenescence in this way, and thus a larval structure may 

 pass over with but little change into the adult. This seems to occur in 

 regard to certain parts of the tracheal system, perhaps is also true of 



* Anat. ADZeig , xx. (1901) pp. 207-19 (1 pi.). 



t Zeitschr. wiss. Zool., lxx. (1901) pp. 171-91 (1 pi. and 4 figs.). 



