100 



(owing to the pigment I suppose for in white featliers it is white) 

 and very long. The outside of the skin shows the dried up horn- 

 sheath round the base of the feather. Often this hornsheath becomes 

 very long; according to Samuel (1871) it may become as long as 

 the feather itself, if the bird is prevented from picking the sheath 

 away. Apparently fullgrown feathers often show, on examination 

 of the inside of the skin, the darkblue calamus and I always con- 

 sidered the latter as a sure sign that the moult had not yet finished. 

 Rests of the hornsheath at the outside sometimes seem to remain 

 for some time after the feather has stopped to grow, but I am not 

 quite sure of this and they never will remain there long after the 

 so called dying of the feather. 



Examination of the outside of the skin is difficult, it costs a lot 

 of time and one can be hardly sure to succeed in finding the last 

 traces of moult. Especially not, if one has to examine those artisti- 

 cally stuffed birds which are the pride of old and even new collections. 



I always examined the inside of the skin of fresh material. 

 Of birds, being prepared for collection-purposes, the whole skin was 

 examined, of most others however — unsightly oilvictims — only 

 the underparts were examined. This was done by giving a length- 

 wise cut from bill to anus, after which the skin on both sides was 

 torn off the flesh as far as the sides of the neck and till above 

 the flanks. By a cut through the ribs at the left side, the genitals 

 were made visible and — if necessary — the testicles were mea- 

 sured or the oviduct prepared out. As an exception the skin of the 

 back was examined and of birds in autumnmoult also the bases 

 of remiges and rectrices at the outside. 



Useful billmeasures were taken of 200 Guillemots. Only fresh 

 material was used for it, in dry skins the bill has dried up and 

 its height is lower accordingly. 



Before coming to the observations themselves I will set forth 

 shortly the method by which the three categories of birds — one, 

 two and three or more years old — were distinguished. 



The one year old Guillemots and one year old Razorbills, as one 

 may expect, do not breed, unless perhaps as a rare exception. 

 This makes it possible to distinguish one year old, two years old 

 and older birds by examination of the genitals: a female which 

 has never laid any eggs, has got an oviduct in the shape of a 

 thread or small band, generally straight; in the female which has 



