No. I.] EMBRYOLOGY OF THE ISOPOD CRUSTACEA. 93 



rise to the eyes cannot be distinguished at this period, nor is a 

 distinctly marked transverse band, such as occurs in Jacra, to 

 be made out. 



Up to this stage sections show no vitellophag cells imbedded 

 in the yolk, but slightly later the immigration of a considerable 

 number of cells of the posterior mesendodermal region takes 

 place, and at about this same time a stout, backwardly project- 

 ing process of the mesendodermal region became visible, and 

 this I take to be the liver endoderm, since it is closely com- 

 parable to the process described in Jaera as the Anlage of the 

 liver lobes. Its origin I have not been able to m.ake out, nor 

 is its fate at all certain, since it quickly disappears, most proba- 

 bly becoming indistinguishable from the mesoderm cells. 



In Fig. 37 is represented a somewhat later stage of develop- 

 ment, in which it is seen that the teloblasts have increased 

 considerably in number, there being now twenty-two of these 

 cells, ten on one side of the center one {cT) and eleven on the 

 other, a disparity of number on the two sides, which is repeated 

 in the specimen from which Fig. 38 was drawn. The source 

 of the teloblasts indistinguishable in the previously described 

 stage (Fig. 36) I have not been able to discover. They do not, 

 however, appear to be formed by the transverse division of the 

 eleven primary teloblasts, and it seems probable that they are 

 due to the addition to the teloblast row of cells lying originally 

 lateral to it, or of the progeny of such cells. Whatever may be 

 the origin of these cells the teloblast row now forms almost a 

 semicircle, enclosing a mass of cells which represent the mes- 

 endoderm. In front and at the sides of the teloblasts are to be 

 seen the teloblastic rows, those on either side of the middle 

 line being a little longer than those further towards the sides, 

 a point which is not well brought out in the figure, it being 

 difficult in it to distinguish between the anterior teloblasts and 

 the most posterior cells of the naupliar region. 



These latter, and the cells in front of them, are characterized 

 by their irregular and scattered grouping, so that they present 

 a marked contrast to the regular rows of the meta-naupliar 

 region. The more anterior cells, however, are more closely 

 aggregated, and form the so-called cephalic lobes of the embryo. 



