72 
Flemming was not able to obtain much information regard- 
ing the history of the digestive tract, but as he has conscien- 
tiously adhered, in his description, (Entwickelungsgeschichte 
der FTajaden), to what he has been able to actually see, his 
account agrees with Babbs so far as it goes, and there is every 
reason to believe that the process is the same in IJnio and 
Anodonta and the oyster. Flemming shows that in Anodon- 
ta the single large macromere divides up into a layer of large 
cells which occupy the dorsal surface of the body, and subse- 
quently become covered by the shell, but he was not able to 
trace their future history. 
The various accounts of the origin of the digestive tract in 
the Cyeladidae are so very contradictory and irreconcilable 
that it does not seem worth while to try to get at the truth 
by comparing them, without making any original observations, 
and Babbs paper and my own fairly represent the present 
state of our knowledge of the origin of the digestive tract in 
Lamellibranchs. The difficulties of observation are so great 
that the observations of an investigator who did not direct 
especial attention to the subject are not likely to afford infor- 
mation of much value, and at the time Loven’s paper was 
written the problems of invertebrate embryology were so dif- 
ferent from those of the present day that no conclusions re- 
garding the history of the digestive tract can be drawn from 
his figures. 
THE DEVELOPMENT OF THE OYSTER AND THE GASTRTJLA THEORY. 
Salensky has given (Bemerkungen fiber Hseckel’s Gastraea — 
Theorie. Arch. f. Haturgeschichte, 1874), a very brief ac- 
count of the origin of the digestive tract in the oyster, illus- 
trated. by three figures. He says, p. 150, “ das erste Stadium 
der Entwickelung ein Embryo ist, welcher aus zwei Schichten 
besteht, und in Inneren keine Hfihle tragt, 55 Figure 1, Taf. 
Y, “ dass sich dann verschiedene aussere Organe und eine 
Mundeinstulpung bilden, und schliesslich im Inneren des En- 
toderms eine Darmhohle entsteht,” Figures 2 and 3. 
After a very exhaustive and able review of the facts in em- 
bryology with which we were at that time acquainted, he con- 
