102 The Neuroglia of the Spinal Cord of the Elephant 
as is best suited for the elements of the organ they support. Neuroglia, 
unlike white fibrous tissue, is found in but one organ and its fibers are 
therefore found in but one general arrangement. Its peculiarities in 
arrangement, then, may be largely imputed to peculiarity of purpose. 
During the latter part of the preparation of this paper, Mall’s inter- 
esting and most necessary paper appeared “ On the Development of the 
Connective Tissue.” ‘This paper deals with all the connective tissues 
except neuroglia. If, after studying the neuroglia in developing ma- 
terial, one reads Mall’s paper, especially the part dealing with the 
development of white fibrous tissue, it will be found that one can cull 
statements from it which, when arranged in sequence, will quite fully 
describe the phases in the development of the neuroglia fibers. For 
the study of developing white fibrous tissue Mall chose the subcutaneous 
tissue of the back of the embryo. In its final arrangement this, of 
course, differs from neuroglia. 
Mall does not mention changes in the connective tissue nuclei simi- 
lar to those above described for neuroglia. His observations, however, 
were necessarily made upon embryos and foetuses alone. Concerning 
the later stages in these he states: “ After the activity of the nuclei 
and endoplasm has produced enough exoplasm to give rise to all the 
white fibers of the skin, which is the case in embryos from 20 to 30 cm. 
long, they cease to be so prominent and sink back into the form of 
irregular cells.” All of the neuroglia nuclei of pigs of 21 cm. and 
below are of the large vesicular variety. In larger foetuses the other 
types begin to appear. At 21 cm. all the nuclei apparently possess more 
or less endoplasm, and nuclei with a large amount of endoplasm are 
much more common than in the adult. Between 16 and 21 cm., the 
neurogha fibers first begin to take the characteristic stain and it is dur- 
ing this period that the processes of myellation go on most rapidly, 
though there are signs of beginning myellation somewhat earlier. Pigs 
at term measure from 26 to 32 cm. 
The dura and pia mater as stainable and indigestible membranes are 
evident long before the neuroglia fibers make their appearance. In 
pigs of 4 cm. they show the characteristic fibrillar structure and though 
thin they both stain by Mallory’s method and resist digestion. Up to 21 
em. the whole spinal cord digests out leaving only a thin cuff—the pia 
mater. At 28 cm. the entire gray figure digests out clean, while in the 
white substance the digestion is less complete. The series of digested 
preparations is not yet finished. 
16Mall. Am. Jour. of Anatomy, Vol. I, No. 3, 1902. 
