856 Aspects of the Body in Vertebrates and Arthropods, | Septem 
that “the brain and nervous cord of the fish or man is funda- 
mentally different, or not homologous with that of the lower or — 
invertebrate animals ;” and then proceeds to criticize it. T 
The chapter on the brain of the locust was written for the un- — 
scientific as well as the scientific reader, and the introductory 
part was presented in a terse, perhaps dogmatic way, for the sake 
of clearness, ee 
The author, without taking time and space to discuss at length 
this broad question, which requires a far wider acquaintance with 
anatomy and embryology than he claims to possess, would beg 
leave to briefly present some facts and considerations which seem a 
to him to support the view he adopted as to the lack of homology 
between the nervous system of arthropods and vertebrates, 
These facts relate to the histology and the histological topog- 
taphy as well as general morphology of the system in question, 
and the general relation of the viscera to the body-walls of arthro- : 
pods as compared with vertebrates. pee 
1. Histology—There are but two histological elements ™ 
brain and spinal cord of vertebrates, 7. e., ganglion-ceis ©” 
nerve-fibers proceeding from them. In worms (and mollusks s0 7 
far as known) and especially in the brain (procerehiiaty t ; 
may call it to distinguish it from the cerebrum of vertebrates) a 
other ganglia of Crustacea and insects, besides these two 
4 
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there is a third substance, the punktsubstanz, discovered per 
dig, and farther described by Dietl and Krieger, and for se 
we would suggest an English equivalent, the myeloid ’ i n 
2. Histological topography.—The arrangement of ap i 
cells and other tissues in the ganglia of arthropods 1s s i post- 2 
ogous with that of vertebrates. In the brain or any of ee 
cesophageal ganglia of arthropods, there is a central me JD 7 
of the myeloid substance, which is enveloped by 4 ail 
of mostly unipolar ganglion-cells. The fibers from the boa? 
cells pass into and emerge again from the myeloid iis 
which is a tangled mass of minute fibrilla. The a 
tain of the ganglion-cells we have clearly seen to pass" rom- 
over the myeloid substance and to form both the erar 
missures of the brain and also the two main longitudinal om ¢ 
sures connecting the chain of ganglia. But the "a to break 
majority of the ganglion-cells appear, as Leydig —_ when cot 
up into the tangled mass of extremely fine fibers, WM" 
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4 
Saab TS 
