i!88 
E. W. MACEHIDE. 
conclusions are like a pyramid standing on its apex! In 
spite of his hostility to me his figures really suppoi’t my 
observations when relieved of the forced interpretation, 
which his espousal of Lwoff has led him to put on 
them. With regard to the formation of the mesoderm 
Cerfontaine has little new to contribute. He dismisses my 
observations with the remark that he has never seen any- 
thing like them in his preparations and that my material was 
badly preserved — -a statement he thinks it necessary to 
reiteiate three times in his paper, and which is absolutely" 
untrue, and especially uncalled for in this case, as Cerfontaine’s 
figures of the formation of the mesoderm are as schematic as 
those which I ]mblished in my first paper. Cerfontaine, 
however, confirms me an-ainst Lwoff in asserting" that 
Amphioxus is an “ enterocoelous” animal so far as the 
cavities of the first pair of somites are concerned. Legros, who 
had previously published a short paper (23) on the larvae of 
Amphioxus, in which he had maintained that the epithelial 
vesicle, identified by Hatschek and myself with the left head 
cavity, was an ectodermal invagination, and that the club- 
.shaped gland had no external opening, followed it up in 
1907 (24) with a paper on the formation of the layers 
in this animal. Legros’s work differs from that of all 
his predecessors in that it is based, not on normal, but on 
abnormal development. By fertilising ova with stale sperm 
and similar means he obtained some curious pathological 
embryos. In one of these there Avas a wide posteriorly directed 
blastopore, but the mesodermal grooves had been already 
formed and from these, two })airs of somites had already been 
separated off. There was also in existence a horizontal ridge 
on each side of the archenteron, tending to divide it into an 
up[)er section to which the ectodermal grooves belonged, and 
a lower one which is l egarded by Legros as consisting of true 
endoderm. When the series of sections w"as followed back- 
wards the horizontal ridges united and shut off the lower 
section of the archenteron, which ended in a cul-de-sac, fiom 
the up])er section, which opened by the blastopore. In 
