32 
MOJ^rCA TAYLOK. 
tissue except at the extreme anterior end of the archinephric 
duct, where a patch of deeply staining mesoderm may possibly 
represent this tissue. 
vStage 27. — At this stage the glomeruli are supplied from 
the coeliaco-mesenberic artery, the pronephros being quite 
ventral to, and much deeper than, the dorsal aorta. The 
pseudo-lymphatic ” tissue has increased, and is no longer 
confined to the anterior end of the kidney rudiment. The 
tissue at this stage consists of scattered masses, deeply stained, 
lying in the neighbourhood of the ducts and blood-vessels. 
Stage 28. — The archinephric duct is more coiled and the 
pronephros has become more posterior relative to the pectoral 
fins. The urinary bladder has increased in length. 
Stage 30. — At this stage the larva is capable of feeding 
and is breathing by means of its gills. Since the first rudiments 
of the mesonephros are barely distinguishable in Stage 29, it 
seems probable that the pronephros is the functional kidney 
at this time. The pseudo-lymphatic tissue has increased 
in bulk, and the rudiments of the mesonephros are larger than 
in the preceding stage. They are segmental structures 
beginning in the twenty-fifth segment, i. e., in the region of the 
posterior half of the archinephric duct, the anterior half being 
quite free from mesonephric tubule rudiments. They consist 
of small, solid knob-shaped masses of deeply staining cells 
quite readily distinguishable from the surrounding “pseudo- 
lymphatic tissue lying mostly dorsal to the archinephric 
duct. Although they seem to develop outwards from the 
immediate neighbourhood of the duct, indenting its otherwise 
straight course, yet they are not formed from the cells of the 
duct, but appear to be condensations of mesenchyme. They 
rapidly increase in size, become moulded into solid twisted 
structures of the nature of solid cords, and eventually acquire 
a lumen secondarily. They extend backwards to the com- 
mencement of the urinary bladder, through eighteen 
segments, i.e., to the forty-third post-occipital myotome. 
Stage 32. — The mesonephric tubules have become hollow 
in most cases, and the cells surrounding the lumen have a 
