272 BULLETIN: MUSEUM OF COMPARATIVE ZUULUGY. 
cells. He therefore concludes “ dass ein wahrer Enterocoelier unter allen 
Chordaten nicht extstirt.” 
I am not able to criticise Lwoff's conclusion from the vantage ground 
of personal investigation of Amphioxus, but his account bears internal 
evidence of careful and exact observation. He calls attention to a fact, 
shown by his figures, that, when the mesodermal pouches arise, spindles, 
if any are present in the mesoderm cells, invariably stand vertically to 
the evaginated layer of cells, foreshadowing an arrangement of the 
daughter cells in two layers. This is exactly the position which the spin- 
dles take during gastrulation in the mesenchyme cells of Ciona, but in 
no other cells of the embryo. The form of division in the mesoderm 
cells of Amphioxus at the period mentioned tends to obliterate the lumen 
of the mesodermal pouches, a result which, as Lwoff's figures show, actu- 
ally comes about. A body cavity is formed only secondarily by the 
moving apart of the mesoderm cells which are arranged in solid masses 
the protovertebree. 
Davidoff (91) likewise observed in the case of the compound Ascidian, 
Distaplia, that spindles stand vertically inthe cells which give rise to the 
mesoderm at the time of the separation of the middle germ layer. He 
believes that the Tunicates can in no sense be regarded as Enteroccelians, 
and, further, that the distinetion made by the brothers Hertwig between 
those Metazoa which possess a “mesoderm” and those which possess 
' is an artificial and unsound one. With these conclu- 
“mesenchyme ’ 
sions I entirely agree. 
Regarding Rabl's (’89) distinction between “gastral” and “peristo- 
mal” mesoderm, my observations lead me to the same conclusion as has 
been expressed by Davidoff, “dass das peristomale Mesoderm der Ascidien 
sich im weiteren Verlauf der Entwicklung zum gastralen herausbildet, 
oder dass das gastrale Mesoderm ursprünglich peristomales Mesoderm ist.” 
O. Hertwig (92) draws a similar conclusion regarding Rabl’s distinction 
as applied to the Vertebrates. 
I should also state that both Lwoff and Wilson (94) find that the 
pole mesoderm cells described by Hatschek in the case of Amphioxus 
do not exist. Certainly nothing of the kind is found among Ascidians. 
Hence we may conclude that such cells are entirely wanting among 
Chordates. 
C. Ancestry of the Chordates. 
To determine the phylogenetic relationship of the Chordates to the 
other groups of Metazoa is a very difficult problem. Various solutions 
