Horn bill Embryos and Nestlings. 539 



Stage I. — 14-days-old embryo of Anthracoceros 

 malayanus. (PI. VJII. figs. 3 & 3«.) 



The disposition of the toes is the only external feature 

 which calls for much notice. The hallux is well separated 

 from the other digits^ but has not yet taken up the backward 

 {)Osition characteristic of the Bucerotidse ; it still points 

 forward and inward. The other digits are still united to 

 eacli other throughout the greater part of their length, the 

 third being a trifle the longest. The plantar surface of the 

 foot is directed outward. There are no traces of feathers, 

 save on the boixier of the pygidium, where one may perceive 

 eight minute papillae, marking the point of exit of the 

 rectrices. The pygidium is acutely pointed and long. 



Dimensions (in millimetres). — Total length 28 ; vipper 

 mandible 2 ; lower mandible 5'3 ; antebrachium 5 ; manus 

 4; tibia 6*2^ foot and tarso-metatarsus 5"5. 



Stage 2. — Nearly ripe embryos of Buceros rlmioceros and 

 Rhytidoceros midulatus. (PL VIII. figs. 1 & 2.) 



Buceros rhinoceros. — The most striking feature of the 

 embryo is its absolute nakedness -, a few feather-papillae may 

 be distinguished with difficulty round the angle of the gape 

 and behind the eye, on the lower part of the back and on 

 the chest, but it is impossible to define very accurately their 

 exact extent. The rectrices and remiges are still invisible, 

 minute depressions marking their future points of emergence. 

 The nostril lies close under the eye and is very small. The 

 upper mandible is large, but no trace of the huge epitheraa 

 of the adult is yet to be seen. Anteriorly it is sharply ridged 

 and abruptly truncated : a slight depression occurs just 

 before the tip ; the sharp edge of the extreme tip must act 

 as an egg- tooth, no actual egg- tooth being present. The 

 lower mandible projects somewhat beyond the upper ; its 

 upper margin is slightly sinuous, and on its extreme anterior 

 edge is a minute papilla. 



The eye-opening is bounded by fleshy, finely-wrinkled 

 eyelids. The cloacal lips are remarkably prominent, but the 

 opening of the oil-gland is not visible ; the pygidium is much. 



