2 Dr. W. Salensky on Héckel’s Gastrea Theory. 
ous types of animals an embryonal form occurs which possesses 
an elongate-oval shape, consists of two layers (exoderm and 
entoderm), and encloses a cavity, the stomachal cavity. Hickel 
discovered a larva of this construction in the Calcispongiz and 
called it the “ Gastrula.” 
“From the identity of the Gastrula in representatives of 
the most different types of animals, from the Sponges to the 
Vertebrata,” Hiickel deduces, ‘in accordance with the bio- 
genetic fundamental law, a common descent of the animal 
phyla from a single unknown stock-form, constructed essen- 
tially in the same way as the G'astrula: the Gastrea’”’*. 
In the monograph of the Calcispongize, however, Hiickel 
adduces but few facts in evidence of his theory. He indicates 
only a few animals in which, in his opinion, this form occurs 
in the cycle of embryonal forms. It would naturally be ex- 
pected that in the memoir subsequently published and specially 
devoted to this theory such facts would be carefully cited ; but 
this is by no means the case. All that he has done for the 
factual establishment of the G'astrwa theory is that he gives 
eight partially diagrammatic figures, and, in the case of certain 
types, mentions some animals in which the Gastrula-stage is 
supposed to occur (see ‘ Die Kalkschwimme,’ Band i. p. 467, 
and ‘ Die Gastrea-Theorie,’ p. 18). The new additions to 
the facts indicated in the monograph of the Calcispongiz relate 
to various types of animals. According to the monograph, 
among the Vermes the Gastrula-stage occurs in Phoronis, Sa- 
gitta, Huaxes, Ascidia, &c., and according to the “ Gastrea- 
Theorie” in the Platyelmintha (Turbellaria and Trematoda), 
the Nematelmia (Nematoda, Sagitta), in the Bryozoa and 
Tunicata, in the Gephyrea and Annelida (Phoronis, Euaxes, 
Lumbricus, Chetopoda). Of the Echinodermata, Hiickel, in 
the “‘ Gastrea-Theorie,” cites, besides the Asterida, the Holo- 
thurida. Of the Arthropoda he says, in the monograph, 
“* Kmbryonal forms which are easily derivable from the G'as- 
trula occur also among the Arthropoda” (Crustacea and Tra- 
cheata). In the ‘‘ Gastrea-Theorie ” he gives the figure of a 
Gastrula deduced from the earliest developmental form of the 
Nauplius. In the Mollusca, the Gastrula is confined, in the 
monograph only, to the development of Limneus ; in the 
“ Gastrea-Theorie ” the Gastrula appears “ to be widely dif- 
fused in the classes of Bivalves and Univalves.” Among the 
Vertebrata Hiickel cites only Amphioxus in both works, al- 
though he remarks that “ the continuity which exists between 
the ontogeny of Amphioxus and the other Vertebrata leaves no 
* Die Kalkschwiimme, Band i. p. 467. 
