4 

 14 THE DEVELOPMENT OP 



Of stage G, my scries of sections is not good enough 

 to show conclusively the steps followed by the entoderm 

 cells at that stage, but in stage If there is no doubt of the 

 part they play. They have become distributed through 

 the yolk, have multiplied rapidly and have begun to ar- 

 range themselves into an epithelium, the lobes of which 

 are not yet continuous with each other. It is difficult (or 

 even impossible) to obtain a single section which will show 

 the relation of these isolated patches of epithelium to each 

 other, but from a series of sections it is clearly seen that 

 at this stage (H)> there are three pairs of well-marked 

 lobes, and that these are from the first distinct from each 

 other. 1 Of these the first, with its mesodermal envelope, 

 abuts directly against the brain and are shown in sections 

 (fig. 59) passing through and just behind the compound 

 eyes. The second pair (fig. 64) are at about the level of 

 the cardiac portion of the stomach, while the third pair, 

 which are the best developed, are just in front of the broad 

 funnel-shaped internal opening of the proctodeum. One 

 of this pair is shown a little out of its proper position 

 with regard to the median line in tig. 54, while in fig. 

 68 the plane of the section cuts across its posterior extrem- 

 ity, and fig. 67 shows that it has a considerable extension 

 towards the sides of the body. All of these lobes are 

 characterized by having the cells well developed and par- 

 taking more or less plainly of the nature of a columnar 

 epithelium, while in the sections which pass between these 

 lobes (e. g., figs. 63, 65) the entodermal cells are scat- 

 tered, and it is difficult, if not impossible, to trace any 

 protoplasmic connections existing between them. 



In fig. 70 is a more careful drawing, on a larger scale, 



'Nusbaum ; ('86) claims that in Oniscus the second pair of liver 

 lobes arise from the splitting of the first pair, and Keinhard ('87), 

 studying Porcellio, confirms him. 



