66 
Tunicates correspond to those of Amphioxus or to those 
of Craniates? The anterior end of the notochord evidently 
cannot help us to answer this question. The restriction 
of the musculature to the tail of Ascidian-larvae and Ap- 
pendicularia evidently has engendered a corresponding 
reduction of the anterior end of the notochord. In the 
“trunk”, the mesodermbands no longer produce muscles but 
only mesenchyme, andasa consequence the notochord is 
no longer required here. In Ascidian-larvae, (KOWALEWSKY 
1871) and newly or unhatched Appendicularia (DELSMAN, 
1910) it is seen still to reach a little distance into the 
trunk, though not as far as under the neuropore, «s is the 
case in Amphioxus; soon afterwards, however, it is exclusively 
restricted to the tail. In a very early stage, however, VAN 
BENEDEN and JULIN (1887, p. 269) remark: „Au début la 
plaque médullaire ne dépassait guêre en avant l'ébauche 
de la notocorde”’. 
The distinctly dorsal, not terminal, situation of the 
neuropore makes us infer that it corresponds to that of 
Amphioxus and to the mouth of the Invertebrate ancestors. 
If this be right the part of the body in front of it may be 
compared with the praeoral lobe of Amphioxus and Annelids. 
This name was already used by WILLEY (1893, p. 328, 
1894, p. 329) for the part of the body lying in front of the 
neuropore and of the mouth. He also compared it with 
the corresponding structure, the snout, of Amphioxus (1893, 
p. 333. Just as in Amphioxus (and in many Annelid larvae), 
the entoderm here is originally in contact with the ectoderm 
but afterwards a space is left between both, representing 
a part of the primary body-cavity. Just as in Annelids and, 
partly at least. in Amphioxus, the mesoderm-cells in this 
cavity proceed from the two mesodermic plates of the 
trunk (while in Amphioxus, the right anterior ‚ntestinal 
diverticulum also provides part of them) We must bear in 
mind, however, that, in giving the name praeoral lobe to this 
anterior body region of Ascidian larvae, WILLEY thinks in 
the first place of the “praeoral lobe” of Balanoglossus trom 
hich in recent times the English speaking zoologists 
are particularly inclined to derive the Vertebrates. However, 
he mentions in this connection the Annelids, Molluscs and 
Arthropods also, to which we of course direct our attention 
in the first place In either case the position of the adhering 
papillae in Ascidian larvae must correspond to the animal 
