THE AMEBIC AN NATURALIST [Vol. LII 



others are probably the result of the environment, since 

 it is well known that nonproductive periods can be in- 

 duced by artificial means. 



One of the most interesting things in connection with 

 the rhythm of egg production as observed by Pearl ( '12) 

 is the existence of hens which never lay an egg, but the 

 record of whose visits to the nests shows a very definite 

 rhythm. A number of such hens have appeared in our 

 flocks. (No*. 5032 and 246. Fig. 13.) The hour of their 

 visits to the nest exhibits exactly the same sort of rhythm 

 as normal hens. These facts point strongly to the ex- 

 istence of some mechanism other than the formation and 

 deposition of an egg which controls the extrusion of the 

 egg. It is interesting to note that if one of these hens is 

 removed from the nest before she is ready to leave, she 

 returns and persists in doing so until, shall we say, she 

 thinks she has laid her egg. Autopsies of several of 

 these hens show that they fall into two classes ; viz., those 

 that are producing yolks or eggs but depositing them in 

 the abdominal cavity, and those in which a tumor of the 

 reproductive system is involved. 



Laying liens often visit the nest at the proper day and 

 hour but fail to lay. Such hens (No. 4529, Fig. 13) usu- 

 ally lay the day previous and the day after in regular 

 routine, though at times they may pay two or more such 

 nonproductive visits in succession. 



A study of these latter records shows that some hens 

 have indications of a potential capacity greater than the 

 actual capacity revealed in the records. Very many hens 

 pay an occasional visit to the trap nest without laying 

 (note the w's in the various records), while a few pay 

 such visits more or less regularly, at various periods of 

 their lives. The striking feature of these visits is that 

 they are made at the hours one would expect if an egg 

 were actually laid (No. 4529. Fig. 13), though the nature 

 of the stimulus that causes such visits is uncertain. 



Broodiness.— Broodiness, from the commercial as well 

 as biological standpoint, is one of the most important of 



