8o MCMURRICH. [Vol. XI. 



consequently have indicated it in the figure as the liver endo- 

 derm il.en). My reason for this belief is derived from the 

 analogy which may be traced between this cell and the cells 

 which give rise to the liver in Astaciis, in which form the ori- 

 gin of the liver has been clearly traced by Reichenbach ('86). 

 After the invaginated cells have begun to assume their vitello- 

 phag function, there is to be seen in the ventral wall of the 

 invaginated sack a layer of columnar cells which do not ingest 

 the yolk-granules, and which form what Reichenbach terms 

 the entoderm plate. From these cells the liver lobes arise. 

 If, as I think must be done, the vitellophag cells of Jaera be 

 compared to the invaginated cells of Astacus, which form the 

 secondary yolk-pyramids, then the relations of the liver endo- 

 derm of Jaera correspond very closely with those of the endo- 

 derm plate of Astacus, a point which may be more clearly seen 

 in the succeeding stages {e.g., Fig. 17). \xv Astac7is \.\iQ vitello- 

 phag cells and the cells of the entoderm plate form a continu- 

 ous layer, but in Jaera the vitellophags scatter irregularly 

 through the yolk, and the continuity of the two parts is broken. 

 Makins: due allowance for this difference, I think there is suffi- 

 cient similarity between the two structures, the liver endoderm 

 of Jaei'a and the entoderm plate of Astacus, to suggest their 

 identity. It is anticipating somewhat to enter upon a discus- 

 sion of the origin of the liver lobes here, but it may be stated 

 that the cells from which they arise in situ \rv Jaera and other 

 Isopods cannot readily be distinguished from the mesoderm 

 cells which lie in their immediate vicinity. As will be seen 

 later, there is a migration forward of the majority of the meso- 

 derm cells to form the mesodermal tissues of the anterior or 

 naupliar portion of the body, and in this migration the cells .of 

 the liver endoderm, it may be imagined, share, taking up their 

 position on each side of the body and proceeding to ingest 

 yolk. In their origin they are closely related to the mesoderm 

 cells and resemble them in appearance, whence the difficulty 

 of distinguishing them, when they have reached their definite 

 position, from the adjacent mesoderm cells. 



In my preliminary notice ('92) of some of the observations 

 recorded in this paper, I described the row of dark cells in the 



