32 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
they lie side by side just beneath the smaller ectodermal elements; 
there appear to be eight longitudinal rows of these neuroblasts which 
extend from the mouth to the anus, and are most clearly differentiated 
anteriorly. The cells proliferate and each soon surmounts a pillar of 
smaller elements, which are the future ganglion-cells. The cytoplasm 
of the neuroblasts is very pale and finely granular and the nuclei are 
pale and refractive, while the daughter-cells stain much more deeply 
throughout and so resemble the elements of the tegumentary ectoderm. 
The “ dotted substance ” makes its appearance in the bases of the lateral 
cords, which are separated by a pyramidal mass of cells, the median 
cord. This mass of cells is headed by another neuroblast, which is 
apparently pushed below the surface by the bulging of the lateral cords. 
While the four lateral neuroblasts represent the cross-section of four 
continuous longitudinal rows of cells, the median cord neuroblasts are 
isolated elements which arise intersegmentally, but soon move forward 
between the two connectives, and finally come to lie just back of the 
posterior commissure in each segment. At a still later stage each is 
incorporated, together with the mass of cells to which it has given I'ise, 
in the posterior part of a ganglion. There is, then, a ninth unpaired 
and interrupted row of neuroblasts extending from mouth to anus. 
The brain and optic ganglia arise as strings of cells budded off from 
sixteen anterior rows in the same manner as the ventral ganglia arise 
from the eight rows of neuroblasts. Like all the cells which they pro- 
duce the neuroblasts are finally inclosed by the outer neurilemma. 
The author desires to emphasize the definite number and arrange- 
ment of the neuroblasts in Xiphidium, because he believes the eight rows 
of the lateral cords to be the homologues of the two rows of cells derived 
from the neuro-teloblasts in Annelids. The homology of the median row 
is a more difficult question, W’hich cannot yet be answered. 
The development of the ganglia from neuroblasts is not peculiar to 
Xiphidium among Insects, for it is quite as distinct in other Orthoptera. 
The “ ganglioblasts ” of Doryphora decemlineata, previously described by 
Mr. Wheeler, are the same as the cells which he now calls “ neuroblasts.” 
Similar cells have been described by other investigators, but none seem 
to have called attention to their definite number, and to their striking 
similarity to Annelid neuroblasts. 
From among his predecessors the author makes reference to the work 
of Korotneff (1885) on Gryllotalpa ; of Graber (1889) on the large cells 
that give rise to the ganglionic thickenings in the dipterous Lucilia and 
the coleopterous Liria and Melolontha ; Patten (1890) found that in the 
embryo of the Scorpion the “ sense-organs ” are arranged in four 
irregular rows in either lateral cord of the ventral chain, and there is a 
single median large “sense-organ”; Viallanes (1890) gives an account 
of the development of the brain in Mantis reliyiosa , which agrees very 
closely with the results obtained from a study of Xiphidium. 
a. Insecta. 
Life-History of Aspidiotus aurantii.* — Mr. A. E. Shipley, who 
undertook an inquiry into the cause of the Orange Disease in Cyprus, 
which is due to this scale insect, gives an account of its life-history. 
* Kew Bulletin, No. 57 (1891) pp. 221-30 (1 pi.). 
