140 THE EMBRYOLOGY OF THE HONEY BEE 



half being then drawn cephalad and caudad respectively into the 

 ganglia adjoining. In HydropJiilus, Lina and Stenobothrus on 

 the other hand the median cord was not observed to separate inter- 

 segmentally from the hypodermis. 



Wheeler's account of the development of the nerve cord of 

 the grasshopper Xiphidium has already been outlined at the be- 

 ginning of this section. The interganglionic sections of the median 

 cord were each represented by a deep invagination, forming a 

 part of the floor of the neural groove, and also by a median 

 neuroblast, the median cord neuroblast. The former, the ecto- 

 dermal invagination, produced no nerve tissue, but remained in 

 connection with the hypodermis and later formed, in the thoracic 

 region, the furcae, apodemes for the attachment of muscles; in 

 the abdomen these invaginations also occurred but persisted only 

 for a short time and then disappeared. The products of the 

 median cord neuroblasts on the other hand become displaced 

 cephalad and contributed to the formation of the posterior me- 

 dian neuromere. 



Heymons (1895) in his researches on the Dermaptera and 

 Orthoptera has virtually confirmed Wheeler's results, as concerns 

 the interganglionic portions of the median cord. Heymons 

 however found instead of one interganglionic neuroblast, several 

 of these cells. In Lepisma Heymons (1897) found that a con- 

 tinuous median cord was set free from the hypodermis and 

 present in the newly hatched nymph, extending the entire length 

 of the ventral cord. 



Carriere and Burger's (1897) statements concerning the fate 

 of the median cord in Chalicodoma are contained in the following 

 paragraphs (pp. 371-372) : "My investigations essentially con- 

 firm the account given by Heymons (1895). Nevertheless 

 I have not been able to determine, that the floor of the neural 

 groove becomes split up into a dermatogenic and neurogenic layer. 

 According to my observations all of its cell material goes to form 

 the median cord, while its covering is produced by the union of 

 the hypodermis formed in the region of the primitive swellings. 



"The complete sundering of the median cord from the hypo- 

 dermis takes place about the end of development. Its intragan- 

 glionic portions separate from the hypodermis at about the same 



