CELLS IOI9 



commonly replaced more or less completely by some special product 

 (such as fat in the cells of adipose tissue, or haemoglobin in the red 

 corpuscles of the blood), in which cases the nucleus often disappears 

 altogether. In the earlier stages of cell-development multiplication 

 takes place with great activity by a duplicative subdivision that 

 corresponds in all essential particulars with that of the plant-cell, 

 as is well seen in cartilage, a section of which will often exhibit in 

 one view the successive stages of the process. 1 Whether * free ' cell- 

 multiplication ever takes place in the higher animals is at present 

 uncertain. 



A large part of the fabric of he higher animals is made up of 

 fibrous tissues, which serve to bind together the other components, 

 and which, when consolidated by calcareous deposit, constitute the 

 substance of the skeleton. In these the relation of the ' germinal 

 matter ' and the ' formed material ' presents itself under an aspect 

 which seems at first sight very different from that just described. 

 A careful examination, however, of those 'connective tissue cor- 

 puscles ' that have long been distinguished in the midst of the fibres 

 of which these tissues are made up, shows that they are the equi- 

 valents of the corpuscles of ' germinal matter,' which in the previous 

 instance came to constitute cell-nuclei, and that the fibres hold the 

 same relation to them that the ' walls ' and ' contents ' of cells do to 

 their germinal corpuscles. The transition from the one type to the 

 other is w r ell seen in fibro-cartilage, in which the so-called ' inter- 

 cellular substance' is often as fibrous as tendon. The difference 

 between the two types, in fact, seems essentially to consist in this, 

 that, whilst the segments of ' germinal matter ' which form the cell- 

 nuclei in cartilage and in other cellular tissues are completely 

 isolated from each other, each being completely surrounded by the 

 product of its own elaborating action, those which form the i con- 

 nective-tissue corpuscles ' are connected together by radiating pro- 

 longations that pass between the fibres, so as to form a con- 

 tinuous network closely resembling that formed by the pseudo- 

 podia of the rhizopod. Of this we have a most beautiful example 

 in bone ; for whilst its solid substance may be considered as 

 connective tissue solidified by calcareous deposit, the ' lacuna? ' and 

 ' canal iculi ' which are excavated in it (fig. 752) give lodgment to a 

 set of radiating corpuscles closely resembling those just described ; 

 and these are centres of ' germinal matter,' which appear to have an 

 active share in the formation and subsequent nutrition of the osseous 

 texture. In dentine (or tooth-substance) we seem to have another 



1 Great attention has lately been given by many able observers to the changes 

 which take place in the nucleus before and during its cleavage. A full account of 

 these is contained in Professor Strassburger's Zellbildung und ZelWteilung, 1880. 

 See also Dr. Klein's ' Observations on the Structure of Cells and Nuclei ' in Quart. 

 Journ. Microsc. Sci. n.s. vol. xviii. 1878, p. 315, and vol. xix. 1879, pp. 125, 404; and 

 chap. xliv. of his Atlas of Histology. The numerous essays of Flemming, in the 

 Archivf. mikr. Anat. from 1875 to 1890 ; Gruber, on the Nucleus of Protozoa, in vol. xl. 

 of the Zeitschr.f. Wiss. Zool.; .and Carnoy, in La Cellule, may be studied by those 

 who desire to carry further the history of the cell. A remarkable series of observa- 

 tions have followed the publication of Professor E. van Bcneden's work on the egg 

 of Ascaris megalocephala in Bull. Acad. Boij. Sci. Belg. xiv. pp. 215-95. 



