90 WHEELER. [Vol. V 1 1 1 . 



of cells. The length of the individual segments is thereby 

 greatly increased and the nerve cord, which is firmly attached 

 in the infraoesophageal region and more loosely in the terminal 

 abdominal segments, is compelled to lengthen. The separate 

 ganglia, besides assuming a somewhat fusiform outline, are 

 scarcely affected by this traction, whereas the connectives are 

 drawn out into thin threads denuded of all ganglionic cells and 

 covered only by the neurilemma. 



The presence in the abdomen of temporary furcal pits cor- 

 responding to the persistent furcae of the thorax admits of an 

 easy explanation, if we take these structures to be correlated 

 with the development of ambulatory appendages. The tem- 

 porary abdominal appendages have usually been regarded as 

 the rudiments of once functional walking-legs, and they are still 

 so well preserved in the Orthoptera that it need not surprise 

 us to find traces of correlated structures which served for the 

 attachment of some of their muscles. 



The progeny of the median neuroblast together with the 

 interganglionic portion of the neural furrow have been ac- 

 counted for; the former becoming the posterior gangliomere, 

 the latter a portion of the sternal integument ; but I have not 

 yet accounted for the remaining portion of the median cord — 

 vh. the intraganglionic walls of the neural furrow. This 

 portion of the groove is crossed by the two commissures and 

 separates those portions of the lateral cord which will ulti- 

 mately constitute the anterior and central gangliomeres. Its 

 cells are of an epithelial nature. Those of the opposite 

 walls of the furrow become applied to one another by the 

 swelling of the lateral cords. The lumen is thereby oblit- 

 erated though its walls are still continuous on the outer 

 surface of the ganglion with the integumental ectoderm. 

 The two lips of the furrow finally fuse and the ganglion 

 together with the portion of the furrow included between 

 its two halves is liberated from the ectoderm. It is these 

 epithelial walls thus set free from the integument which 

 appear to give rise to the outer and inner neurilemmata. 

 Both these neural envelopes are ectodermal ; there are no 

 traces of mesodermal structures taking any part in their forma- 



