18 GENERAL PHYSIOLOGY. 



therefrom (we shall see farther on whether the nerve glob- 

 ules are derived from the external or the intermediate fold 

 of the blastoderm). 



The internal fold will give, by means of the envelopment 

 which forms the internal cavity of the embryo, the internal 

 cuticle, or the epithelium of the future intestinal canal of 

 the embryo, and also the numerous adjuncts of this canal, 

 most of the glands, and also the lungs. 



The globules of the intermediate folds undergo transfor- 

 mations which are much more complicated ; some are trans- 

 formed, by the mechanism already mentioned when treating 

 of the globules in general, into muscular, nervous (perhaps 

 also into nerve cells) elastic, and connective fibres, and other 

 forms of the connective tissue ; others remain in the condition 

 of globules, though changing their form ; and again others 

 become fused with the fibrous elements of the connective 

 tissue (embryonic globules, cells of cartilage, of bone and of 

 tendons) and others bathe in a liquid (blood globules) ; thus, 

 in short, the intermediate gives origin to two globular forms, 

 viz., the embryonic cell and the blood globule (and possibly 

 the nerve-cell.) l 



The elements of the external cuticle, and those of the 

 internal cuticle or internal epithelium being then united in 

 the single term epithelial (or lining) globules, since they line 

 the surfaces 2 , we have but four kinds of globules to study, 

 viz., the epithelial, the nerve, the blood, and the embryonic 

 globule. 



1. Epithelial globules, placed upon fibrous membranes, 

 destined only for their support, form the sole living portions 



ing to whether it covers all the superficial parts of the body or the 

 cavities communicating with the exterior, it is either internal or 

 external. 



1 This distinction of the hlastodermic cells may at first seem 

 surprising, though a similar phenomenon is continually passing 

 under the observation of every surgeon. In a fresh superficial 

 wound, there appears first a mass of globules, primarily alike, 

 which separate themselves so as to become either epiderm-cells, 

 connective fibre, etc., before the cicatrix is formed, and exactly in 

 the same way as in the folds of the epiderm. 



2 In fact, the word " epithelium " was primarily used to designate 

 the epiderm of the nipple, and afterwards to designate the epiderm 

 of the mucous membrane, to which there is now a tendency to limit 

 its application. 



Astruc says : " La peau fine et delicate qui recouvre le mamelon, 

 et qu'on appelle Epithelion " (eTn, 6rj\f) ; upon, the nipple). 



