No. 3.] NEUROBLASTS IN THE ARTHROPOD EMBRYO. 34 1 



the intersegmental region where the original ectodermic layer 

 has been less affected by neural differentiation. The absence 

 of median neuroblasts in front of the mouth is easily accounted 

 for by the high degree of concentration and the lack of inter- 

 segmental spaces in the three pairs of ganglia that constitute 

 the brain. 



The development of the ganglia from neuroblasts is by no 

 means peculiar to XipJiidium among insects ; it is quite as dis- 

 tinct in other Orthoptera. In the common locust {Melanoplus 

 feniJir-rubrum) I can detect the same number of rows of prolif- 

 erating cells both in the ventral nerve-cord and in the optic 

 e-ano-lia and brain. In Xiphidimn and Mela^iophis all stages 

 in the proliferation of the neuroblasts may be observed m a 

 single embryo ; in the brain the columns of cells attain a con- 

 siderable length before the neuroblasts in the terminal segments 

 have budded off more than one or two cells. 



Blatta germafiica presents essentially the same conditions as 

 Mclanoplus. 



The " frandioblasts " of Dorvphora decemlineata described in 

 a former paper are the same as the cells which I now call 

 "neuroblasts." Re-examination of my preparations has con- 

 vinced me that in this insect also the number of rows is 

 approximately four for either lateral cord. I fail, however, 

 to detect a definite string of cells extending inward from each 

 terminal cell; still there can be no doubt that the irregularly 

 arranged ganglion cells are budded off from the neuroblasts. 

 Doryphora, a highly modified form even among Coleoptera, 

 would be expected to present in the development of its nervous 

 system characters less primitive than those of the Orthoptera. 



Neuroblasts in insect embryos have been described and fig- 

 ured by other investigators, but no one, to my knowledge, has 

 called attention to their definite number and to their striking 

 similarity to Annelid neuroblasts. Korotneff, in his paper on 

 Gryllotalpa} figures four neuroblasts in the lateral cord in 

 two cases (PL XXX, Fig. 60; PI. XXXI, Fig. 61). He 

 also describes the manner in which they differentiate from the 

 primitive ectoderm and proliferate to form ganglion cells (p. 

 589). His figures are taken from embryos too old to show 



1 Zeitschr. f. wiss. Zool., Bd. 41, 1885. 



