■ 222 M. IN ABA. 



Vertel)rate,s consist of two substances distinct in tlieir ovig-in. This 

 Braun " hns confirmed in Reptiles, and Mitsiikiiri ' in Mammalia. 

 Mitsukuri says that in the 16th day embryo ral)bit the medullary 

 substance is already distinct ; sympathetic nerve cells closely applied 

 to the inner side of the suprarenal blastema send in a process partly 

 composed of nerve fibres into the ventral end of the suprarenal ; the 

 cells thus carried in become gradually transformed into the medulla, 

 (iottschau* and Janosik'' dispute this statement. TlnMigh these 

 authors do not deny the entrance of the nerve fibres into the 

 suprarenal, they state that the two jiarts of the suprarenal substance 

 cannot be distinguished at the time of the entrance, and the medullary 

 substance is gradually ditterentiated from the cortical substance at a 

 considerably later stage, Gottschau even states that in some mam- 

 mals the medulla is developed only after birth. Yet fivMn the descrip- 

 tions of the two authors, the exact nnxle of the formation of the 

 medulla is not yet clear, and it is also necessary to trace the ultimate 

 fate of the nervous fibres sent into the suprarenal Idastema. 



The suprarenal blastema is already distinct in the 13th day 

 embryo. It is a somewhat elongated mass of cells lying between 

 the 16th and 17th l)ody-segnients, just behind the lobes of the 

 lun^'s. The anterior end of the l)lastema lies on about the same 

 level as the 2nd tubule of the mesonephros, while the 3i'd segmental 

 tul)ule lies on ab(out tl>e middle portion of the suprarenal. In 

 cross sections ( wooden r 3 and V\. XXX. fig-. 8), the blastema 



2. F>au und Entwicklung der Nebennieren bei Reptilien. Arb. aus dem Zoo]. Zoot. Inst, 

 in Wurzburg. Bd. V. 1882. 



;î. On the Development of the Suprarenal Bodies in Mammalia. Quart. Journ. of Mic- 

 roscop. Science, XXII. 1882. 



4. Structur uad embryonale Entwiclclung der Xe))ennieren bei Silugethieren. Arch. f. 

 Anat. u. Physiol. 18S3. 



5. Bemerkungen libn- die Entwicklung der Xe})enniere. Arch. f. Mikr. Anat. XXII. 

 1883. 



