The pronephros of Scyllium canicula. 261 
of the rudiment to the ectoderm on the left side of this and neighbouring 
sections. 
Fig. 30 (Section 2,27). The nephrocoel on the left side in this 
figure is enlarged. A comparison of this fig. with the preceeding and 
two succeeding figs. shows how the pronephros seems to be inserted into 
the somatic mesoderm more and more dorsalwards the further caudalwards 
we pass. 
Fig. 31 (Section 2,28). This shows the typical condition of the 
pronephros in the region of proto. VIII at this stage. The true groove- 
like nature of the rudiment is disguised by an outpushing of the splanchnic 
mesoderm of the lateral plate, whereby the coelom between the lateral 
plates is obliterated in the pronephric region. 
Fig. 32 (Section 2,29). On the left side in this figure the nephrocoel 
seems to extend into the pronephros; RABL would speak of this coelomic 
extension as an ostium. Notice how the pronephros now seems to be an 
outgrowth of the nephrotome, not of the lateral plate; this is however not 
the case. 
Fig. 33 (Section 2,30). Passes through the posterior region of 
segment VIII on each side. 
Fig. 34 (Section 2,31). Notice the relations existing between proto- 
vertebra, nephrotome, lateral plates and pronephros in this figure. 
Fig. 35 (Section 2,32). The distal portion of the rudiment on each 
side is assuming the appearance of a solid duct, although it is still 
connected with the mesoderm. There is a trace of a pronephrie artery 
on the left side of the figure. 
Fig. 36 (Section 2,33). On the left the pronephrie duct is shown 
free from the mesoderm, and contiguous, but not fused with, the ectoderm. 
There is no sign of an isolated „Sammelrohr“, such as RABL figures for 
Pristiurus. 
late 21. 
Fig. 37 (Section 2,34). The pronephros is very prominent in this 
region, viz. at the level of somite IX. 
Fig. 38 (Section 2,35). In this section and the next, one 
can observe most clearly that the ectoderm is quite distinct from the 
pronephric duct. 
Fig. 39 (Section 2,36). On the right side of this figure there is 
visible what VAN WIJHE and RABL would perhaps interpret as a „Vor- 
nierenostium“, but a reference to neighbouring figures renders this most 
improbable. 
Fig. 40 (Section 2,37). Passes through the hinder end of seg- 
ment IX. 
Fig. 41 (Section 2,38). In the next section or the next but one to 
this the left pronephric duct becomes separated from the mesoderm. 
the 
