TRANSFORMATIONS UNDERGONE BY NUCLEI. 125 



Batrachians, a complete network of nerve-tubes is formed by this junction 

 and coalescence of the processes from branching cells : a similar observa- 

 tion was also made by Schwann.* According to Schaffner, as the nerve- 

 tubules coalesce and increase in size, the walls of the cells from which they 

 originate are gradually drawn out and merge into those of the tubules, 

 while their granular contents also become continuous and identified with 

 the contents of the tubules. 



In considering the transformation which cells undergo in the develop- 

 ment of tissues, too much stress cannot be laid on the importance of the 

 share taken by the nuclei in these changes, especially since this appears to 

 have been entirely overlooked by Schwann. It is proposed, therefore, to 

 bring together some of the more striking circumstances which seem to 

 demonstrate the importance of nuclei, whether considered as individual 

 structures, or as component parts of cells. That the nuclei may exist in 

 tissues apparently independent of cells, has been shewn especially by the 

 observations of Mr. Paget,f who found that many morbid growths are 

 composed almost entirely of corpuscles like nuclei or cytoblasts. These 

 morbid structures were usually tumours of very rapid growth, and from 

 the almost invariable presence of large quantities of nuclei, it would 

 seem that they must play an important, if not the chief part in this 

 growth. The abundance of nuclei in most, if not all, other actively grow- 

 ing tissues, healthy as well as morbid, their persistence in those tissues, 

 such as the muscular, in which a constant waste and repair consequent on 

 the active discharge of their function is taking place, their invariable 

 existence in the secreting cells of all glands and epithelia, and their 

 disappearance from the cells of fat, which when fully formed cease to 

 perform any active function, all attest the importance of the share taken 

 by the nuclei in the processes of growth, reproduction, and secretion. 

 Equally strong confirmation of this is furnished also by the variety of 

 examples in which development, in either structure or composition, is 

 effected in the animal organism by cells unprovided with nuclei, while 

 there are many instances in which nuclei, whether contained in cells or 

 without them, appear to assume higher forms, or to be centres and sources 

 of formative and reproductive power. { The evidence of these facts is based 

 chiefly on his own observations on tumours above alluded to, and on the 

 investigations of Professors Henle and Goodsir,|| and of Mr. Simon. H" 

 The researches of the last-named observer on the glands without ducts, 

 tend to prove the discharge of a large amount of gland-function by nuclei 

 alone; for in the thymus, the splen, and other such glandular organs, 



* Mikroscopische Untersuchungen, p. 177. 



*t" Report on Anatomy and Physiology for 18445, p. 35. 



J Mr. Paget, Lectures at the Royal College of Surgeons, May 1847. Lecture 5. 



Allg. Anat. pp. 192 9. || Anatomical and Pathological Observations, 1845. 



11 A Physiological Essay on the Thymus Gland, 1845. 



