266 THE AMERICAN NATURALIST.  [VOL. XXXIII. 
and the description of the membrana tectoria as a cuticular structure 
(p. 890), may be contrary to fact, but they are blemishes which dis- 
appear in the marvelous wealth of accurate information which fills 
the whole work. i 
The place that the new Anatomy will find is not difficult to predict. 
Its size and fullness, together with the heaviness of Gegenbaur’s style, 
will probably prevent it from being a popular text-book with most 
beginners, but its masterly qualities will make it an absolute neces- 
sity to every advanced student of vertebrate anatomy. In this 
respect it will occupy the field formerly held by Wiedersheim’s 
Lehrbuch, though it seems to us unlikely that it will replace in any 
extensive way this author’s Grundriss, which from its elementary 
character and simple language makes so satisfactory a book for 
the beginner. 
The heavy debt which vertebrate anatomists already owe to Gegen- 
baur is materially increased by this accession to the list of best text- 
books, and it must be the wish of every one that circumstances may 
favor the early completion of a work destined to be so scholarly and 
valuable a contribution to the comparative anatomy of the verte- 
brates. GHP 
The Natural History and Morphology of Dero vaga.'— This 
interesting little aquatic worm was described twenty years ago by 
Dr. Joseph Leidy? in this journal as Au/ophorus vagus. It is found 
in shady places among vegetation in ponds and ditches, living by 
preference among masses of floating Lemna or among alge on the 
bottom, shifting its position gradually from surface to bottom or 
vice versa, according to the location of food supply. Its food consists 
of vegetable matter, principally desmids, alge, and even the fronds 
of Lemna. The worms inhabit cases which they construct of stato- 
blasts, Arcella shells, the leaves of Lemna, etc. The cases of indi- 
viduals living at the surface float, and those of individuals living at 
the bottom sink when the worms are removed. The period of 
sexual reproduction occurs during the first two weeks of July, when 
the body cavity posterior to the clitellum is crowded with eggs. 
Asexual reproduction by fission takes place throughout the year, but 
most rapidly during warm weather, when it may occur as often as 
1 Brode, H. S. A Contribution to the agane of Dero vaga, Journ. of 
Morph., vol. xiv (1898), pp. 141-180, Pls. XIII-XV 
2 Leidy, J. Notice of Some Aquatic Worms " oe Family Naids, dm. Nat., 
vol. xiv (1880), pp. 421-425. 
