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 caecum vitplli ; this 

 sliows 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 distiniiuished as meso- 

 gi/rous. The number of turns in such a spiral depends directly 

 upon the length of the intestine ; whilst in the short-gutted Sylviae 

 the spiral is just indicated, there are in the Sparrow (with an 

 intestinal length of 21 centim.) Ig direct and 1 retrograde turns, and 

 in Pinicola enucleator {^\\\\c\\ 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 Limic-olse, Laridse, and Columba? likewise to assume 

 the niesogyrous 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 niesogyrous 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 loo|) remains 

 straight. This feature may be termed telogyrous. With the duo- 

 denum this is very rare, it then invariably forms a right-handed 

 spiral, e. g., in Buceros, Ciconia, Milvtis ; the duodenum is more 

 irregularlv 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 

 bv 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 convolutions 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. In 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- 

 ccelous feature (fig./, 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 



