42 1 8DMMAUY OF CURRENT RESEARCHES RELATING TO 



the grade of development of the oi-frans councctLd therewith ; and 

 especially with that of the enteric caual He directs especial attention 

 to the fact that, in the Anura examined by him, from the earliest 

 appearance of the coelom in a purely cellular mesoblast until the 

 c()mpleti()n of the metamorpliosis, there was not the least indication 

 of the process which His says he has directly observed in the fowl ; 

 of course, at a later period, new elements were intercalated among 

 those already pi'csent in the epithelium of the ccelom ; these cells 

 arise from a decj)er mesodermal layer, but they become completely 

 assimilated with the epithelium already develojied, and it is impossible 

 to distinguish between younger and older elements. 



In giving an account of the formation of the coelom attention is 

 specially directed to the following points : brown })igment was not 

 confined to the epiblast and its derivative, the central nervous system, 

 but was also found in the endoblastic cells surrounding the primitive 

 enteric cavity, in the notochord, and in the i)rimitive vertebrae. The 

 cavity of the so-called hepatic diverticulum, the base of which is lost 

 by the absorjition of the yolk-cells there placed, is bridged over by 

 epiblast in the neighbourhood of the ventral middle line. In Bufo 

 cinereus the ccelom first appears in the most anterior dorsal portion of 

 the mesoblast, niesially to the pronephros. In the hinder part of the 

 body, where the mesoblast is still unelcft, there is a linear and, later 

 on, a spindle-shaped cleft which is triangular in form, directed orally, 

 and at first quite symmetrical. Nearer tlie head the ccelom is asym- 

 metrical, for on the right its transverse diameter is longer than ontho 

 left. As long as the ccelom forms a cleft its cellular investment does 

 not difier in form from the other cells of the mesoblast. The flattening 

 out of the coelomic epithelium is to be ascribed to mere mechanical 

 causes. 



The changes in the visceral peritoneal epithelium in the region of 

 the enteric canal were studied in Pelohates and Hana ; as the cells 

 continue to branch the elongation of the enteric canal goes steadily 

 on ; when the metamorphosis is complete new elements appear be- 

 tween the now large cells of the coelom and new elements make 

 their way among them. In Rana, after the completion of the meta- 

 mor])hosis, when the enteric canal has reached its last degree of 

 degradation, a new period of growth begins, which has, as may be 

 supposed, some influence on the visceral ccelomic epithelium. This is 

 expressed by the protrusion of processes, and by the appearance of 

 rounded granular elements which take their place in the interspaces 

 of the cell-mosaic ; these last appear to arise from a layer deeper 

 than that of the coelom-cpithelium, and to gradually force their way 

 to the surface. 



In the third chapter of his essay the author gives examples of 

 changes in the form of cells of the coelomic epithelium, which are 

 due to an adaptation to subjacent structures, but these can hardly be 

 rendered intelligible without the assistance of figures. 



The visceral, pleural, and pericardiac epithelia are next considered, 

 and then the stomata of the mesentery. As tTie Amphibia appear to 

 have close phylogonetic relations to the C'yclostomata there are some 



