26 LIBBIE H. HYMAN. 



abnormalities. I may here report a number of abnormal chicks 

 obtained from eggs unintentionally left in the incubator room 

 for several days before being placed in the incubator. The 

 temperature of this room is about 30 C., a temperature at which, 

 as is well known, the hen's egg will develop slowly for some time. 

 These eggs were incubated about thirty hours: all of the chicks 

 alive at the end of this period, about one dozen, were abnormal. 

 The growing region of the primitive streak was in all cases 

 inhibited to a greater or less extent. In most of the embryos it 

 formed one or more irregular projecting masses of cells. As a 

 result of this inhibition of the primitive streak, the posterior 

 half of these embryos is too short and with too few somites as 

 compared with the anterior half. One of these embryos is 

 illustrated in Fig. 48. The anterior half of this embryo is normal 

 (except the heart) but posteriorly the primitive streak terminates 

 in a large projecting mass. On the right side the number of 

 somites is about normal for the state of development of the 

 anterior end but on the left side the number is considerably 

 reduced. The posterior end of the neural tube is inhibited: the 

 tube is widely open and the neural folds poorly developed 

 especially on the right side. As already stated, eleven other 

 embryos with similar conditions of the posterior end were 

 obtained. Of these twelve embryos the anterior end appears 

 entirely normal except in two cases where the head is exceedingly 

 abnormal represented only by a crumpled mass at the level of 

 the heart, the heart being then located anterior to this mass. 

 This condition was called omphalocephaly by Dareste. One of 

 the two embryos of this type obtained is illustrated in Fig. 49. 

 The posterior end is nearly normal but the greater part of the 

 head is invaginated into a mass containing crumpled fragments 

 of neural tube. This mass is situated to the left of the embryo. 

 The heart is at the anterior end. In the majority of these 

 embryos the heart is abnormal. 



The most complete description of abnormalities in the chick 

 is that of Dareste in his well-known book. As Dareste found 

 that all experimental procedures induce practically the same 

 types of anomalies, he does not state in his description how 

 the different abnormalities were produced. He lists the following 



