showed that the three
divisions of the coelom arise as pouches constricted off from the
archenteron or primitive gut, thus resembling the development of the
mesoblastic somites of _Amphioxus_. It would appear that while the direct
development throws light upon the special plan of organization of the
Enteropneusta, the indirect development affords a clue to their possible
derivation. However this may be, it is sufficiently remarkable that a small
and circumscribed group like the Enteropneusta, which presents such a
comparatively uniform plan of composition and of external form, should
follow two such diverse methods of development.

_Distribution_.--Some thirty species of _Balanoglossus_ are known,
distributed among all the principal marine provinces from Greenland to New
Zealand. The species which occurs in the English Channel is _Ptychodera
sarniensis_. The _Ptychoderidae_ and _Spengelidae_ are predominantly
tropical and subtropical, while the _Balanoglossidae_ are predominantly
arctic and temperate in their distribution. One of the most singular facts
concerning the geographical distribution of Enteropneusta has recently been
brought to light by Benham, who found a species of _Balanoglossus_, _sensu
stricto_, on the coast of New Zealand hardly distinguishable from one
occurring off Japan. Finally, _Glandiceps abyssicola_ (_Spengelidae_) was
dredged during the "Challenger" expedition in the Atlantic Ocean off the
coast of Africa at a depth of 2500 fathoms.

AUTHORITIES.--W. Bateson, "Memoirs on the Direct Development of
Balanoglossus," _Quart. Journ. Micr. Sci._ (vols. xxiv.-xxvi., 1884-1886);
W. B. Benham, "Balanoglossus otagoensis, n. sp," _Q. J. M. S._ (vol. xlii.
p. 497, 1899); Yves Delage and Ed. Herouard, _Traite de zoologie concrete_
(t. viii.), "Les Procordes" (1898); S. F. Harmer, "Note on the Name
Balanoglossus," _Proc. Camb. Phil. Soc._ (x. p. 190, 1900); T. H. Morgan,
"Memoirs on the Indirect Development of Balanoglossus," _Journ. Morph._
(vol. v., 1891, and vol. ix., 1894); W. E. Ritter, "_Harrimania maculosa_,
a new Genus and Species of Enteropneusta from Alaska," Papers from the
Harriman Alaska Exhibition (ii.), _Proc. Washington Ac._ (ii. p. 111,
1900); J. W. Spengel, "Die Enteropneusten," _Eighteenth Monograph on the
Fauna und Flora des Golfes von Neapel_ (1893); A. Willey, "Enteropneusta
from the South Pacific, with Notes on the West Indian Species," _Zool.
Results_ (Willey), part iii., 1899; see also