370 NATURAL SCIENCE. june. 



have departed furthest from the common type. The resemblance 

 which Dr. Gadow claimed for the intestinal convolutions between the 

 Falconiformes and Ciconiiformes, Mr. Mitchell seems unable to 

 support. 



The superiority of Mr. Mitchell's system of studying the intestinal 

 convolutions lies in its greater simplicity. It now remains for him 

 to follow the example of Dr. Gadow, and to group into a series of 

 types the various methods of stowing away the intestines, a task by 

 no means easy, and only to be attempted after further research. 



The Hoatzin. 



In his second paper, "a contribution to the anatomy of the 

 Hoatzin, OpistJioconms cristaius," which appeared in the Proceedings of 

 the Zoological Society for June, i8g6, Mr. Mitchell adds a few facts 

 concerning the intestinal convolutions and certain of the muscles of 

 the visceral skeletal apparatus, and of the leg. 



The intestinal convolutions have been studied after the fashion 

 just described. As a result it is found that the mid-gut presents a 

 definite divergence from the primitive arrangement. Thereby it is 

 more specialised than in the Galliformes or Struthiones, in which the 

 primitive type is very nearly retained. It seems intermediate between 

 Ptevocles and the pigeons, but presents many points in common with 

 the cuckoos, thus adding another to the many features common to 

 these latter and Opisthocomus. 



In spite of the fact that the myology of Opisthocomus has been 

 described already by Garrod and Perrin, Mr. Mitchell has succeeded 

 in bringing to light many new points. The most interesting of these 

 deal with the variations of the ambiens muscle, a subject which has 

 already engaged much of the author's attention ; indeed, he was the 

 first to point out the existence of the ambiens, in a vestigial condition, 

 in forms in which it had hitherto been supposed to have been lost. 

 This will be best appreciated by those who know the important place 

 held by this muscle as a taxonomic character. Opisthocomus furnishes 

 us with an example, so far unique, of a species in which the ambiens 

 has been found in every gradation from complete development to a 

 mere vestige. "Apart from possible systemic value, it is of interest 

 to find variations of so great magnitude in a few specimens of a bird. 

 Professor Weldon has recently shown, after examination of an 

 exceedingly large number of individuals of shore-crabs that very 

 slight deviations may be associated with a larger death-rate. In the 

 case of creatures so difficult to shoot as Opisthocomus it may be the 

 case that those actually examined have, from the greater magnitude 

 of their variations, been less able to escape." 



The '* Index Animalium." 

 The number of species of recent animals already described has 

 been computed by our Zoological Recorders as 386,000 ; including 



