Descriptioii of the Modifications of certaiii Organs. 643 



Fig. 16—17 represeut the stouiadi of an Ostricli chick, about 3—4 

 days old, in its natural position and sliape. It contained already some 

 grass and a few sniall sliarp edged pebbles in the proventriculus and 

 in the gizzard, none larger than half a pea. The glandulär area was 

 still oval and only slightly elongated or stretched; the blindsac of 

 the proventriculus looked tailwards, as does its opening into the 

 gizzard. The specula of the latter were already distorted out of 

 thcir normal position, but to a snialler extent th;;n in the adult. The 

 course of the gastric branches of the N. vagus likewise indicated 

 a torsion. 



The following measurements will show that, taking the breadth 

 of the gizzard as the Standard for comparison of increase in growth, 

 in . the chick as well as in the adult the increase of ef is smallest, 

 whilst the length cd, i. e. the elongation of the proventricular sac iu- 

 creases most Avith age. 



or. 



In Order to show that the amount and the nature of the food, to- 

 gether with other material, influences the shape of the stomach, re- 

 ference to a few other birds is necessary. 



Cormorants and Herons swallow their food, consisting of fishes, 

 Wholesale; the stomach is thinwalled and highly elastic; the two tri- 

 turating muscles, so typical of the avine stomach, are very weak, but 

 the two tendinous specula are still present. The stomach attains 

 a great size, taking up the greater portion of the body cavity. — We 

 cannot assume that such an arrangement existed in the ancestral Ste- 

 ganopodes and Herodii, because, although descendants of fisheating 

 birds themselves, there exist other Steganopodes, like Pelecanus, with 

 small and more normally avine stoniachs, whilst the fish are stored 

 up in the enlarged gullet ; nioreover the stomachs of young Cormorants 



