744 SUMMARY OF CURRENT RESEA.BOHES RELATINa TO 



In those eggs of the Aphides which develope parthenogenetically there 

 is only one directive corpuscle, and therefore only one directive amphi- 

 aster; in the eggs that require fertilization there are two quite normal 

 directive bodies. Weismann has made a similar observation with regard to 

 the summer eggs of Daphnids, in which there is only one directive 

 corpuscle. 



Post-embryonal Development of Muscidse.* — Prof. A. Kowalevsky 

 observes that in the larva (and even in those which have just escaped from 

 the egg) of the Muscidse we find the rudiments of a number of organs which 

 have no function in the larval stage ; these imaginal organs develope more 

 slowly than those which are functional in the larva. In addition to the 

 already well known imaginal discs we find special imaginal rings and cells 

 for the enteric canal, and special cells and groups of cells which form 

 afresh the muscles of the imago. Ectoderm, mesoderm, and endoderm have 

 their proper imaginal rudiments, which do not predominate in development 

 until after the metamorphosis of the larva ; when the pupal stage arrives 

 the growth of the larval organs is ended, and the larval skin and muscles 

 are inactive ; they are now useless and are a disturbing element for the 

 developing imaginal body, but they are seized and destroyed by the 

 phagocytes. Special observations were made on the muscles, glands, and 

 hypodermal cells ; the muscles have the same appearance as in the larvse, 

 and the hypodermal cells have absolutely the same structure, so that we 

 cannot have to do with dead or dying organs. The contents of the nuclei 

 escape from them in the same way as the contents of the cell of Spirogyra, 

 when attacked by Vampyrella, and this shows us that we have to do with 

 living nuclei. As the whole phenomenon was studied in stained prepara- 

 tions and sections, the author thinks it well to add that the tissues and 

 organs seized by the phagocytes exhibit the same relation to the staining 

 reagents as do the functional organs of ripe larvse ; were these tissues dead, 

 the appearance would be different. 



The fact that the phagocytes do not seize on the freshly forming organs 

 and tissues, but only upon those whose function is accomplished, shows us 

 that the developing and actively living organ is not seized upon by the 

 phagocytes; there must, in fact, be a certain functional weakness which 

 permits of the organs being attacked by phagocytes. It is more difficult to 

 explain the case of the fat-cells, but it may be suggested that these cells 

 lose their power of assimilation dtu'ing the metamorphosis, and so come 

 into the category of weakened organs. The fact that the useless organs are 

 not simply cast off, but eaten, digested, and converted into a fluid condition 

 for the developing organs, is an example of the economy of the organism. 

 All larvae which cannot use up these weakened organs require more fat and 

 other reserve material than those which use their muscle and larval integu- 

 ment just as if it were a prepared food ; the latter is clearly the more useful 

 method. 



Histology of Insect Muscle.f — Herr E. v. Limbeck has investigated 

 the histological differences between the two different kinds of muscles which 

 can be readily distinguished in insects, even with the unaided eye. The 

 observations of Eetzius and Bremer, which by no means agreed with those 

 of previous investigators, prompted the author to submit the facts to fresh 

 examination. His material was always taken from freshly killed animals 

 and treated in various ways. The muscles were sometimes frozen and cut 

 at right angles to their axes, or treated with L6 wit's gold-formic acid 



* Zeitschr. f. Wies. Zool., xlv. (1887) pp. 542-94 (5 pis.), 

 t SB. K. Akad. Wiss. Wien, xci. (1885) pp. 322-49 (I pi.). 



