26 
MONICA TAYLOR. 
pylorus and duodenum. The blind, pocket-like outpushings, 
mostly on the ventral side in the beginning, can easily be 
seen at this stage, growing forward more oi- less parallel with 
the pyloric part of the stomach, in the mesodermal covering 
of the canal. (In PL 4, fig. 24 a transverse section through 
the valve at Stage 35 is given.) 
The special character of the pyloric valve just described 
and the study of its development suggests one or other of the 
following hypotheses : 
(1) That these finger-like outpushings of the duodenum 
represent degenerating pyloric caeca, or — 
(2) That pyloric caeca have been evolved by an elaboration 
of these caecal ontgrowths consequent upon their becoming 
free from the muscular coat of the alimentary canal. 
An examination into the condition of pyloric caeca in Teleo- 
steans seems to furnish evidence in favour of either interpre- 
tation. Many Teleosteans are without pyloric caeca, and the 
number of these caeca when present and their arrangement is 
extraordinarily varied. 
Among Ganoids, Acipenser, the most primitive, is 
possessed of pyloric caeca. It is interesting to note that 
the early appearance of the caecal rudiments, as described by 
A. Nicholas (7), recalls the adult condition of the pylorus 
arrangements in Sy mb ranch us, only, that in the case of 
Acipenser, the outpushings of the duodenum, while directed 
towards the stomach, do not fuse with the walls of the latter 
— the muscular coat of the alimentary canal is involved in 
the outpushing. 
In Amia the pyloric caeca are absent, but the pyloric 
valve, as described by Piper (8), resembles quite closely that 
of Symbranchus. 
Among Teleosteans the pyloric valve of the eel, where 
pyloric caeca are abseut, is of the Symbranchus type. 
Pyloric caeca are absent in Cyprinoids, Labridae, Gobiiae, 
Bleunidae, Syngnathus and Cob it is — forms in which there 
is no obvious stomach. In Blenn ius pholis and Carassius 
auratus there is no specialisation of the pyloric valve, there 
