Semi-Centennial Volume. 99 



Abnormalities Produced in the Nervous System of the 

 Chick Embryo. 



Florence Alsop. 

 Contribution from the Zoological Laboratory, Kansas State Agricultural College (abstract). 



Abnormalities were produced in the nervous system of the chick em- 

 bryo by incubating the eggs under different degrees of heat. Some of the 

 eggs were kept in low temperatures ranging from 94°-101° F. Others 

 were incubated at 104'-108" F. Different periods of time were used 

 with all the temperatures, varying from twenty-two to seventy-two hours 



The most noticeable abnormality found in embryos subjected to tem- 

 peratures below normal for twenty-four hours, was the lack of folding 

 in of the neural plates for some distance above and below the primitive 

 knot region. The neural folds in the anterior end of the embryo were 

 generally formed, and these folds extended posteriorly as far as the 

 first somite. Below this point until the primitive node region was 

 reached the flattened neural plate only was developed. At this place the 

 folds appeared again. Not only was the tube formed here, but also extra 

 thickenings of the walls of the tube, and numerous cells, apparently of 

 ectodermal origin, nearly filled the central canal. In some specimens the 

 tube was closed entirely, and in others the excessive tissue filled the canal 

 in such a way that two or three neural openings were present in it. This 

 condition was found more frequently in the forty-eight and seventy-two 

 hour chicks than in those incubated for a shorter length of time. 



Another abnormality produced at low temperatures was the curved 

 primitive streak. This was seen in the early stages of development. In 

 these instances the neural folds turned off to the left side of the embryo 

 and formed a curved tube. 



A third condition produced was the formation of one neural plate into 

 a neural fold before the other had begun to develop. This lack of develop- 

 ment of the neural fold appeared more often in the younger specimens 

 than in the older, because the other neural plate finally formed after a 

 longer period of incubation. 



Embryos produced under excessive heat developed different types of 

 deformities than those formed at low temperatures. A large per cent of 

 the abnormalities appeared in the head region. A constriction of the 

 neural tube below the optic vesicles occurred frequently. The optic 

 vesicles and midbrain developed much more rapidly than that part of 

 the brain between them, until a very small neck connected the two. 



The effect of high temperatures upon the somites was the reverse of 

 that caused by low temperatures. Nearly four per cent of the embryos 

 incubated at 104'-108' F. developed extra somites lateral to the ordinary 

 somites, while in those embryos produced below 101" F. the number of 

 somites was diminished, or did not form at all in some of the twenty- 

 four hour chicks. 



In those eggs incubated at 94°-101° F., sixty-seven per cent were ab- 

 normal. Seventeen per cent of these abnormalities were in the brain 

 region. Eighty-three per cent were in the neural tube. 



