ORIGIN OF DISEASE AND THE GEIIM THEORY. 145 



more detached lobulated bits of cartilage. Moreover, in the 

 axilla there were also similar detached nodules of cartilage. 



The cases of supra-scapular developments brought before the 

 Royal Medical and Chirurgical Society of London by Mr. Willett 

 and Mr. Walsham were also similarly regarded. Supernumerary 

 fingers, too, have been supposed to point backwards to the many- 

 rayed Selachian fin. 



Again, new formations of capillary vessels are as a rule 

 congenital, and they are also much more generally met with in 

 the skin of the head and neck than elsewhere. These two facts 

 may suggest the possibility that they are in some degree homo- 

 logous with the vessels which develop about the epiblastic 

 involutions lining the visceral arches of the lower vertebrata. In 

 support of this idea it may be remarked that Dr. D. A. Gress- 

 well recently observed in a patient a noevus which extended in a 

 snake-like manner down the right s|de of the neck. The noevus 

 was distinctly raised, and, tapering towards its upper extremity, 

 it passed down the external auditory meatus for some distance. 



Having considered some of the indications seen among some 

 abnormal structural phenomena of higher animals which remind 

 us of remote ancestral conditions, we now, in pursuance of the 

 same line of argument, proceed to consider some special facts 

 connected with the early division of the cells which make up the 

 developing embryo of a higher animal into the three separate 

 divisions known as the embryonic layers. 



The lowest living beings consist simply of undiflferentiated 

 protoplasm, almost identical throughout, both in regard to form 

 and in regard to functional capacity. The next stage in animal 

 life is that which is represented by the Diploblastica, in which 

 there are two distinct layers of protoplasmic units, either of 

 which is in some measure capable of discharging the functions 

 of the other. A third stage is that displayed by the Triplo- 

 blastica, in which each of the three layers is largely independent, 

 both in regard to structure and in regard to function, and is by 

 no means capable of taking on the functions of another layer. 



Similarly, stages comparable to these are passed through in the 

 early development of the embryo of any higher animal, the three 

 layers being known respectively as the epiblast, the mesoblast, and 

 the hypoblast. Now, the resemblance which attaches itself to 

 those parts of higher animals which have been developed from the 



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