ral
eminence. The ciliated epidermis, the long worm-like form, and the
complete absence of segmentation of the body-muscles lead us to forms
like the Nemertines. The great proboscis of _Balanoglossus_ may well be
compared to the invaginable organ similarly placed in the Nemertines.
The collar is the first commencement of a structure destined to assume
great importance in _Cephalochorda_ and _Craniata_, and perhaps
protective of a single gill-slit in _Balanoglossus_ before the number of
those apertures had been extended. Borrowing, as we may, the nephridia
from the Nemertines, and the lateral in addition to the dorsal nerve, we
find that _Balanoglossus_ gives the most hopeful hypothetical solution
of the pedigree of Vertebrates."

Much doubt was cast upon the Chordate affinities of the Enteropneusta by
Spengel in his monograph of the group,[422] but when the development of
the coelom came to be more thoroughly worked out in _Balanoglossus_ and
Amphioxus, the striking resemblance in this respect between the two
forms gave additional support to the Batesonian view.[423]

[386] The stages in the development of microscopical
technique are well summarised by R. Burckhardt,
_Geschichte der Zoologie_, p. 121, Leipzig 1907.

[387] "Entwickelungsgeschichte des Amphioxus lanceolatus,"
_Mem. Acad. Sci. St Petersbourg_ (Petrograd) (vii.),
xi., No. 4, 1867, 17 pp., 3 pls.

[388] "Weitere Studien ue. die Entwickelungsgeschichte des
Amphioxus lanceolatus," _Arch. fuer mikr. Anat._, xiii.,
pp. 181-204, 1877.

[389] Particularly by Hatschek (1881) and Boveri (1892).

[390] "Entwickelungsgeschichte der einfachen Ascidien,"
_Mem. Acad. Sci. St Petersbourg_ (Petrograd), (vii.),
x., No. 15, 1866, 19 pp., 3 pls. "Weitere Studien ue. die
Entwicklung der einfachen Ascidien," _Arch. f. mikr.
Anat._, vii., pp. 101-130, 1871.

[391] _Descent of Man_, i., p. 205, 1871.

[392] _Arch. f. mikr. Anat._, vi., 1870, and viii., 1872.

[393] _Archives de Biologie_, 1884, 1885, and 1887.

[394] _Bull. Acad. Sci. St Petersbourg_ (Petrograd) xiii.,
1869, and _Zeits. f. wiss. Zool._, xxii., 1872.

[395] _Mem. Acad. Sci. St Petersbourg_(Petrograd)(7),
xix., 1873.

[396] Giard, _Arch. zool. exper. gen._, i., 1872, and
Lacaze-Duthiers, _ibid._, iii., 1874.

[397] For the later history of the Amphioxus-Ascidian
theory the reader may be referred