306 DR. H. GADOW ON THE INTESTINAL [May 21, 
loops. In many instances a spiral is produced by one loop being 
curled upon itself, its apex then forming the centre of the spiral. 
On to the apex is attached the diverticulum cecum vitelli; this 
shows that this spiral is produced by the primitive fold uf the em- 
bryonic mid-gut. 
Such is the case in all the Passeres, and since there are only three 
folds formed by the whole gut, the spiral represents the middle or 
second fold; hence this arrangement may be distinguished as meso- 
gyrous. The number of turns in such a spiral depends directly 
upon the length of the intestine ; whilst in the short-gutted Sylvize 
the spiral is just indicated, there are in the Sparrow (with an 
intestinal length of 21 centim.) 13 direct and 1 retrograde turns, and 
in Pinicola enucleator (which possesses an intestine of 99 centim. in 
length) there are many direct turns. 
It is clear that with an original number of only four loops, the 
conversion of the two middle ones into one spiral will cause such 
birds as certain Limicole, Laride, and Columb likewise to assume 
the mesogyrous feature; but the position of the diverticle on the 
original third loop, and the relations of these birds, like, e. g., 
Charadrius and Sterna, show that this mesogyrous formation has 
been brought about in a way different from that of the Passeres. 
Lastly, the distal portion of any loop originally straight may 
become coiled up into a spiral, whilst the rest of the loop remains 
straight. This feature may be termed ¢elogyrous. With the duo- 
denum this is very rare, it then invariably forms a right-handed 
spiral, e. g., in Buceros, Ciconia, Milvus ; the duodenum is more 
irregularly twisted in certain Pelargi and Accipitres. The ends of 
the second, third, and fourth loops are never coiled up into a regular 
spiral, but rather form irregularly coiled up masses, in many 
Pelargi, Accipitres, and in the Psittaci. 
We see, then, that the cycloccelous (meso- or telogyrous) feature 
by itself cannot be taken as a character which indicates the affinity 
of the larger groups or orders of birds, unless we take the mode of 
development of these concentric conyolutions into consideration. 
In fact the cycloccelous formation is the highest mode of stowing 
away in the smallest compass that portion of the gut which had to 
be increased in length, the relative length of the mid-gut being” 
dependent upon the nature and composition of the food. Tn strictly 
orthoccelous birds the increased length of the gut causes the for- 
mation of secondary folds anywhere between the previously existing 
loops, whereby frequently a very irregular arrangement of all the 
convolutions is caused. A similar process has produced the plagio- 
celous teature (fig. f, p. 305), which was probably derived from an 
orthoccelous basis. 
The highest and perhaps newest mode of stowing away an 
increased amount of intestinal length is that in which one of the 
folds already existing is lengthened and, owing to its interstitial 
growth, turns into a spiral ; in this way the other loops will undergo 
the least possible disturbance, 
I do not think it necessary to give here a long and detailed 
