238 T. H. Burzenn, 
Embryo H. 
6'/,, mm long. 45 or 46 protovertebrae. Mounted upon 6 slides 
having respectively 74, 74, 75, 75, 75 and 78 sections. 
Left side Right side 
1,64—2,14 Ear 1,64—2,15 
2,47—2,60 1 2,49— 2,62 
2,61—3,1 II 2,63—3,1 
3,2—3,11 III 3,2—3,12 
3,12—3,22 IV 3,13—3,23 
3,23— 3,32 V 3,23 — 3,33 
3,33—3,43 VI 3,34 — 3,44 
3,44—3,53 Vil 3,44—3,54 
3,54—3,62 VIII 3,54—3,63 
3,64—3.72 IX 3,64—3,73 
3,74—4,7 x 3,73 —4,8 
Segmentalbläschen in segs. IT?, III, — about XVI. 
On the left side the pronephros extends as far forwards as 
3,44: the duct separates from the underlying mesoderm at 3,68, and 
ends at 5,23. Thus the pronephric somites are VII, VIII and 
anterior portion of IX: the duct has now grown back to the front 
end of XXIII. Traces of pronephric arteries in sections 3,42 to 
3,46, and in 3,52 to 3,55. 
On the right side the rudiment begins at 3,45; the duct becomes 
distinct at 3,69, and ends at 5,13. Hence the organ occupies the 
same region of the body on each side in this embryo as in Embryo G, 
but the duct only reaches back to seg. XXI on the right side. 
The first right pronephric artery is present between VI and 
VII (sections 3,42—3,46) and the second in sections 3,52 to 3,55. 
Embryo I. 
6'/, mm long, the tail end being much twisted. 67 or 68 proto- 
vertebrae. Mounted upon 3 slides having 174, 133, and 104 sections 
respectively. 
Left side Right side 
1,86—1,113 Ear 1,87—1,113 
1,155—1,166 I 1,155—1,165 
1,165 — 2,5 II 1,164— 2,4 
242,19 III 23-218 
