316 s. H ATTA : 



and the distal portion (a.2)n.2) constitutes the Anlage of the 

 pi'onephros — the name I assigned to the same in my preliminary 

 paper ('97). To avoid tiresome reiteration, 1 shall often speak 

 of them in the following pages simply as the " xinhige " and when 

 it is necessary to refer to special ones, as ihe Anlage lirst, the 

 Anlage second, etc. in tlie order of their position in t1ie series of 

 mesoblastic somites, beginning from the anterior end. 



In the somite next following, i.e. the sixth (fig. 5), the 

 mesoblast shows almost the same condition as that already des- 

 cribed ; but in the somite preceding the fifth, i.e. in the fourth, 

 the Anlage of the pronephros is a little more advanced in 

 development (fig, 3). On the left side of fig. 3, the fourth 

 myotome is sliced only at its hind wall {mt.IV), while, on the 

 light, it is cut through in the middle {mt.IV). On the right 

 half of the section, no marked progress is visible in the meso- 

 blast except the separation of the myotome, which shows a pen- 

 tagonal outline {mt.IV) and consists of high cylindrical cells 

 from the lateral plate formed of a loose mass of cells {hi.). In 

 the left half, however, the state of things is quite otherwise : 

 the Anlage of the pronephros {a.pn. 1) together with the corres- 

 ponding visceral layer is entirely constricted off from the myotome 

 {ml. IV), although it. is still connected with the lateral plate {Im.). 

 The cells composing the Anlage are compactly set together and 

 arranged more or less in a radial manner ; the Anlage itself is 

 rounded off at the proximal end. The lateral plate, on the other 

 hand, still consists of loosely grouped cells of variable shape. 



The Anlage is thus always (before and after its separation 

 from the myotome) histologically very distinct from the lateral 

 [)late ; one might therefore often be misled to suppose that there 

 is no organic connection between these two structures. 



