318 SUMMARY OF CURRENT RESEARCHES RELATING TO 
cessive modifications of the brachial apparatus in Terebratella dorsata 
and Magellania venosa , find that certain stages have often such a per- 
sistence that their transitory stages may be considered as distinct genera 
or true species. The first stage they call the premagadiform ; the 
succeeding stage has a striking resemblance to the Magas-type ; then 
follows that which Dali showed to be characteristic of his genus Maga- 
sella, on which follow the Terebratella , and in some the Magellania- 
stages. 
Basing themselves on these views, the authors give tables to show 
the relations of various species to one another. 
Arthropoda. 
Nerve-centres of Arthropoda.* — M. H. Viallanes, who commences 
his sixth memoir on this subject with an account of the brain of Limulus 
polyphemus, gives the following table, which summarizes a number of 
important points : — 
1st segment. 1 
Protocerebrum J 
Crustacea. 
lOptic and psychical 
Insects and 
Myriopods. 
centre innervating 
Arachnida and ' 
Limulus. 
the eyes. 
Centres provided with 
prae- oesophageal com- 
missures. 
2nd segment. ] 
Deutocerebrum ' 
f Olfactory centre. 
| Innervates 1st pair 
of antennas. 
( Furnish a root 
Olfactory centre. 
Innervates antennae. 
to the visceral 
Tactile centre. 
Innervates cheli- 
cerae and rostrum, 
nervous system, j 
3rd segment. 
Tritocerebrum 1 
f Antennary lobe. 
Tactile centre. 
Innervates 2nd pair 
of antennae. 
Wanting. 
Wanting. 
Centres provided with post-oesophageal 
commissures. 
(Esophageal 
ganglion. 
Gustatory centre. 
Innervates labrum. 
Furnishes a root to 
the visceral nervous 
k system. 
(Esophageal 
ganglion. 
Gustatory centre. 
Innervates labrum. 
Furnishes a root to 
the visceral nervous 
system. 
Wanting. 
4th segment. 
1st suboeso- 
phageal ganglion 
| Inner- 
vates 
mandibles. 
The author’s studies lead him to propose the following scheme of 
classification of the Arthropoda :- 
( Antennata 
Arthropoda 
Chelicerata . 
j Biantennata 
I Quadriantennata . . 
I Myriopoda. 
Peripatus. 
Iusects. 
Crustacea. 
( Limulus. 
\ Arachnid a. 
Ann. Sci. Nat., xiv. (1893) pp. 405-5G (2 pis.). 
