26 SUMMARY OF CURRENT RESEARCHES RELATING TO 



morphosis through a Hemichthys-st&ge. (7) The young eels enter the 

 streams during spring, about two years after their parents entered the 

 sea. 



Against these conclusions must be placed what we do not yet know. 

 We do not know the history between the larva of 15 days and the 

 Leptocephalus stage ; we are uncertain in regard to the egg and the 

 early development ; we do not know whether the eggs are normally or 

 only occasionally pelagic ; we are unaware of the normal habits of the 

 Leptocephalus ; we have not yet secured a female with eggs larger than 

 <)*27 mm. in diameter — far from maturity ; the question whether the eel 

 ever breeds in fresh water must be still considered undecided. 



b. Histology. 



Text-Book of Comparative Histology.* — K. C. Schneider has done 

 a good piece of work in writing his text-book, which, apart from Oppel's 

 large treatise (confined to the alimentary tract), is the first compre- 

 hensive treatise on comparative histology since Leydig's classic work 

 published about fifty years ago. The first part of the book is general 

 cytology and histology ; the second part — called Architektonic — is 

 really general morphology ; the third and largest part gives an account 

 of the minute structure of the tissues from Sponges to Vertebrates. 



Molecular Structure and Histology. f — M. Heidenhain seeks, in a 

 somewhat difficult essay, to show that the minute structure of muscle- 

 fibrils — both in transverse and longitudinal section — admits of being 

 interpreted in terms of molecular architecture. 



Theory of Cell-Division.! — A. Giardina expounds what may be 

 called a chemico-physical theory of cell-division. He supposes currents 

 of diffusion from the centrosome, — currents of specific substances which 

 have a chemotropic, chemotactic, action on the hyaloplasm. The karyo- 

 kinetic figure is not a figure of lines of force, but a figure of lines of 

 diffusion in two distinct fluids, in which spindle and aster represent two 

 distinct dynamic systems. The function of the nucleus is not active, 

 but passively regulative. Most important is the centrosome, which acts 

 as a centre of diffusion. 



Trophospongium of Nerve-Cells and Pancreatic Cells. § — E. 

 Holmgren has previously described intracellular canaliculi {Saftkanal- 

 ihen) in various kinds of cells. In close association therewith are the 

 intracellular nets, which he calls trophospongia, well seen, for instance, 

 in the spinal nerve-cells of the rabbit. From the multipolar " intra- 

 capsular " cells, whose protoplasmic processes surround the nerve-cell 

 proper like a basket, there arise fine branches which penetrate the nerve- 

 cell and form an intracellular network or trophospongium. Similarly in 

 the glandular cells of the salamander's pancreas, there is an intracellular 

 net, restricted to the region between the nucleus and the gland-lumen. 



* ' Lehrbuch der vergleichenden Histologie der Tiere.' Jena, 1902, 8vo, xiv. and 

 1*88 pp. and many illustrations. 



t Anat. Anzeig., xxi. (1902) pp. 391-8 (1 fig.). 



X Tom. cit., pn. 561-81 (4 tigs.). 



§ Arch. Mikr.' Anat., lx. (1902) pp. 669-SO (1 pi. and 3 figs.). 



