230 
pronephrie region of this embryo. 
T. H. BurtenD, 
recognizable condition of the organ. 
Left side 
The figure shows the earliest 
The following table gives the extent of the anterior segments: 
Right side 
1,52—1,68 Ear 1,61—1,75? 
1,76—1,89 it 1,82—1,95 
1,91—1,104 mM 1,96—1,106 
1,106—1,115 III 1,107—1,116 
1,116—1,124 IV 1,117—1,124 
1,125—1,133 Vi 1,125—1,133 
1,134—1,143 VI 1,134—1,143 
1,144—1,153 VII 1,144—1,153 
1,154—2,4 VII 1,154— 2,4 
2,5 —2,12 IX 2,5—2,13 
2,13— 2,20 X 2,14—2,21 
The total number of protovertebrae in this embryo was 23 or 24. 
The neurenteric canal was present in sections 2,126 to 2,134. Seg- 
ment XXIII extended over sections 2,96 to 2,101 (left side) and 
over 2,94 to 2,97 (right side). 
In this embryo the nephrotome region in segments III to X 
or XI is very prominent owing to the presence of large nephrocoels 
(Segmentalbläschen), which van Wie also noticed in Pristiurus 
embryos. These structures seem to be homologous with the so-called 
“innere Vornierenkämmerchen” of FELIX. 
An examination of the serial sections will reveal the fact that 
the earliest trace of the pronephros is a continuous, and not a 
segmental structure (as van WIJHE and Rückerr have claimed), 
which is quite as prominent in the inter-segmental regions as it is 
in the segmental regions. 
Embryo B. 
31, mm long. 25 protovertebrae. Fixed in corrosive acetic, and 
stained in Boraxcarmine. Mounted upon 2 slides having 161 and 
144 sections respectively. (The number before the comma in the 
table below indicates the number of the slide, the number after the 
comma is that of the particular section on the slide.) 
Left side 
1,69—1,85 
1,87—1,106 
Ear 
I 
Right side 
1,63—1,82 
1,84—1,105 
