2 Dr. \V. Salensky on HiicheVs Gastra^a Theory. 



ous types of animals an cniLryonal form occurs which possesses 

 an elongate-uval shape, consists of two hiyers (exoaerm and 

 entoderm), and encloses a cavity, the stomachal cavity. }l;ickel 

 discovered a larva of this construction in tlic Calcispongite and 

 called it the " (nustntla.'' 



" From the identity of the Gastnda in representatives of 

 the most ditferent types of animals, from the Sponges to the 

 Vertebrata," Iliickel deduces, " in accordance with the bio- 

 genetic fundamental law, a common descent of the animal 

 })liyla from a single unknown stock-form, constructed essen- 

 tially in the same way as the Gastrula: the Gcuitrwa^^*. 



In the monograph of the Calcispongia?, however, Iliickel 

 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 s])ecially 

 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 Gastrwa theory is that he gives 

 eight partially diagrammatic figures, and, in the case of certain 

 types, mentions some animals in which the Ga^trula-stage is 

 supposed to occur (see ' Die Kalkschwiimme,' Band i. p. 467, 

 and ' Die Gastra^a-Theorie,' p. 18). The new additions to 

 the facts indicated in the monograph of the Calcispongiai relate 

 to various types of animals. Accordi)ig to the monograph, 

 among the Vermes the Giist/'ula-stage occurs in Phoroms, Sa- 

 i/itta, Euajces, Ascidia, &c., and according to the " Gastrsea- 

 Theorie" in the Platyelmintha (Turbellaria and Trematoda), 

 the Nematelmia (Nematoda, Sagitta), in the Bryozoa and 

 Tunicata, in the Gephyrea and Annelida {Plioronis, EuaxeSy 

 Lwnbricus, Chaitopoda). Of the Echinodermata, Iliickel, in 

 the " Gastrea-Theorie," cites, besides the Asterida, the Holo- 

 thurida. Of the Arthropoda he says, in the monograph, 

 " Embryonal forms which are easily derivable from the Gas- 

 trula occur also among the Arthropoda" (Crastacea and Tra- 

 cheata). In the " Gastrsea-Theorie " he gives the figure of a 

 Gastrula deduced from the earliest developmental form of the 

 Naitplius. In the Mollusca, the Gastrula is confined, in the 

 monograph only, to the development of Limiuius ; in the 

 " Gastraea-Tlieorie " the Gastrula appears " to be widely dif- 

 fused in the classes of Bivalves and Univalves." Among the 

 Vertebrata Hackel cites only Amphioxus in both works, al- 

 though he remarks that " the continuity which exists between 

 the ontogeny of Ampldoxus and the other Vertebrata leaves no 



* Die Kalkscliwamme, Band i. p. 407. 



