168 GEORGE W. TANNREUTHER 
blast into two equal parts, right and left (figs. 40-41). These 
two cells, for convenience in description, will be called the pos- 
terior right and left proteloblasts. At the fifth division each 
proteloblast buds off a small cell, x‘, external to x! and x? re- 
spectively (fig. 44). At the sixth division each of the protelo- 
blasts buds forth a small cell, x° on either side of x*, beneath 
the derivatives of c! and d! (text fig. 8). At the seventh division 
each of the proteloblasts buds off a small cell, x® on the ventro- 
anterior edge at the junction of the two cells (fig. 46). 
At the eighth division each proteloblast, on either side of the 
median plane of the embryo, divided into two equal parts (figs. 
47, 48, 93). The four cells formed become the posterior telo- 
blasts, X® and X®, right and left of the median axis (fig. 47). 
X‘? without any further division, becomes the neuroblast on either 
side, and X° becomes the nephroblast on either side of the median 
axis (figs. 47-48). Next X®, right and left, divides equally, 
giving X and X® (figs. 50, 52). Next either X or X‘* divides 
equally. If X divide, which is the common occurrence, we get 
X® and X™. But if X” divide instead of X, the final result 
is the same. In either case, we get four teloblasts on each side 
(one neuroblast and three nephroblasts) as shown in figures 
56 and 57. Next X® on either side divides very unequally and 
gives rise to x7 on the anterior ventral outer surface (fig. 49). 
The progeny of the ‘first somatoblast,’ when the teloblasts 
are completely formed, is twenty cells. Table 2 shows the 
derivatives of the ‘first somatoblast.’ 
TABLE 2 
x 3 
KEXEX? ay pee Gab Gap 
-el/ V U wa 
DKK (a) 
ee Eb Sse!) EE 
Proteloblast Proteloblast 
