OBSERVATIONS ON THE NERVOUS SYSTEM OF APUS. 437 
It is the small ganglion situated between the brain and the 
mandibular ganglion, a little before the first postcesophageal 
commissure. To that ganglion come, on one side, the fibres of 
this commissure; on the other, the fibres of the stomatogastric 
nerve. In another Phyllopod, a neighbour of Apus, Limnetis, 
I think this ganglion may be seen in the swelling in front of 
the mandibular ganglion, a little behind the ganglion of the 
second antenna . 1 
This ganglion has been considered as the first postcesophageal 
ganglion of the abdominal cord . 2 
I think that it cannot be homologized with the ganglia of 
the cord. In consequence of the great development of the 
stomatogastric nerve, it is easily understood that a ganglion 
appears on the point where it joins the ventral cord. We have 
not here a segmental ganglion; it is only an adventitious one. 
Its lateral position in Apus is a proof of this statement. It 
belongs more to the enteric system than to the somatic. 
Nevertheless there are, in the abdominal cord, ganglia 
situated before the mandibles. They are : the ganglia of the 
second pair of antennae, the existence of which we have just 
ascertained, and the ganglia that we shall see in the brain, 
and from which come the nerves of the first antennae. 
III. — It is necessary to study the histological structure of 
the brain of Apus, and the disposition of the ganglionic cells, 
to show if it is an archicerebrum or a syncerebrum. 
The brain of Apus is small and thin, and can be studied 
by transparency. But I tried the method of serial sections 
after embedding in paraffine, to obtain more exact and precise 
results. I used as colouring Kleinenberg's haematoxvlin. I 
have made transverse (bilateral vertical) and longitudinal (an- 
tero-posterior horizontal) sections. By means of Caldwell's 
microtome I obtained complete series of sections. But, the 
brain of Apus being very small, I found some difficulty in 
obtaining vertical transversal sections, and I have used prin- 
1 Grube, “ Bemerkungen fiber die Phyllopoden,” * Archiv fur Naturg.,’ 
1853. 
3 Gegenbaur, ‘ Manuel d’Anatomie comparee,’ p. 352. 
