28 



yolk of birds appears in the human umbilical vesicles I have studied. 

 Branca alone among recent workers claims as much for man. Yolk 

 has been reported for the sacs of some of the higher mammals — e. g. 

 mouse and rat by Robinson (38), and hedgehog by Hubrecht (20) — 

 but no undisputed observations have been made for the human um- 

 bilical vesicle. Though the histologic structure of the entodermal 

 cells might permit of absorption, there is no yolk to absorb. Their 

 only function can be one of secretion. 



Another attempt to argue for the nutritive function of the 

 human umbilical vesicle is made by Branca as follows: "Qu'on con- 

 sidere un organe rudimentaire , cet organe subit des ph6nomenes de 

 regression qui portent sur la morphologie externe comme sur la struc- 

 ture. La reduction de sa taille coincide avec I'atrophie de ses elements. 

 Et il en est ainsi non seulement pour les organes rudimentaires (6pi- 

 physe, notocorde etc.), pour les organes dont on lie les voies d'ex- 

 cr6tion (testicule) mais aussi pour les organes, comme la raamelle, qui 

 subissent, et parfois ä maintes reprises, les phenomenes de regression. 

 Et s'il est vrai que la function cr6e I'organe, on doit admettre qu'une 

 fois la fonction disparue, I'organe disparait a son tour .... il ne 

 faut point juger I'importance d'une fonction ä sa duree". 



But, 1) granting that the higher mammals have descended from 

 ancestors with yolk-bearing eggs, the human umbilical vesicle must 

 be considered as at least a partially rudimentary structure. 2) Though 

 it has suffered a reduction in size, this need not necessarily imply an 

 "atrophy of the elements", but perhaps simply a reduction in number, 

 e. g., as in the vermiform appendix. 3) The epiphysis is usually re- 

 garded as a vestigial structure, but its elements are not atrophied. 

 The cells that in reptilian ancestors functioned as light receptors have 

 disappeared, but the remaining elements retain a healthy state, and 

 may possibly function in the elaboration of an important internal se- 

 cretion just as the hypophysis has been experimentally proved to do 

 by Gushing (9) and others. 4) The notochord cannot be regarded 

 as a case in point. There is here no analogy between a rudimentary 

 organ (supposing the umbilical vesicle to be strictly rudimentary) and 

 a necessary embryonic organ. The notochord, having fulfilled its 

 special function, disappears just as do Meckel's cartilage and the 

 lanugo hair, etc. 5) The testicle grows smaller in old age and the 

 spermatogonia! cells atrophy, but interstitial cells may remain healthy 

 and function long after the termination of sexual potency. The organ 

 grows smaller, but all of its elements do not necessarily atrophy. 

 6) The mammae bear no sufficiently close analogy to a rudimentary 



