INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 693 



noticed that, as tlie cell itself became constricted preparatory to 

 division, pseudopodial filaments stretclied across the small space be- 

 tween it and its neighbours, these processes being sometimes so 

 numerous as to form a sort of fringe. 



The ordinary epidermic cells showed no intracellular network, but 

 amongst them were found a greater or less number of cells in which 

 this network was remarkably well developed. These " reticulate cells " 

 (Netzzellen) are often twice as large as the others, and of a more 

 rounded form ; they have compact, oval nuclei, which, as usual, may 

 become broken up into filaments, all stages between the two conditions 

 being observed. Nuclear filaments were seen to extend between those 

 of the intracellular network, but no actual connection of the two 

 seems to have been observed. 



The reticulate cells are formed from those of the usual character 

 by a network appearing around the nucleus, and gradually extending 

 to the periphery. They may return to the ordinary condition by a 

 reversal of the process : the filaments of the network undergoing 

 gradual fusion, from the periphery inwards. 



The entire process of division took two hours and a half in the 

 ordinary, one hour and a half in the reticulate cells. In both cases 

 three-quarters of this time was occupied in the division of the nucleus, 

 one-quarter in that of the cell-body. The process is thus a slow one, 

 not as in plant cells, according to Strasburger, rapid. 



The series of events which together constitute the division process 

 are as follows : — The nucleus, first of all, undergoes a considerable 

 increase in size ; next, there appear in it a few lumps or granules, 

 some larger, some smaller ; the number of these increases ; they 

 lengthen out, and form short, finer or coarser filaments, which are at 

 first scattered without any definite arrangement, and intermixed with 

 unaltered granules through the nucleus. The number of the granules 

 decreases, the filaments become longer, the contours of the nucleus 

 vanish, and the filaments group themselves, sometimes about a centre, in 

 more or less regular forms, producing the filamentous difterentiated 

 nucleus of authors. 



Development of the Ribs and the Transverse Processes.* — Herr 

 Fick is of opinion that the ribs have an independent and separate 

 origin to the superior arches of the vertebrte ; and that, likewise, the 

 transverse processes are not budded off from the superior arches, but 

 are difi'erentiated from the tissue that lies to the sides of the cartilage 

 of these parts. Taking as an example the third myocomma, he shows 

 that towards its i^eripheral end there is a rounded tongue of cartilage, 

 which, decreasing in size, extends towards the chorda; at its most 

 central end there are distinct cartilage-cells, and the whole structure 

 is separated from the surrounding muscular tissue by a layer of 

 spindle-shaped nuclei, which seems to form the embryonic perichon- 

 drium ; from this the " superior arch " is in section seen to be dis- 

 tinctly separated. 



* ' Arch. Anat. und Eutw.' (His and Braune), (1879) p. 30. 



