80 MARINE BIOLOGICAL LABORATORY. 



form (Haeckel, Lankester, Balfour, Blitschli, and Met- 

 schnikoff). 



Von Ihering suggests^ the possibility of the trans- 

 formation of a multinucleate protozoan into a metazoan 

 by the segregation of the protoplasm around the various 

 nuclei, whereby the organism becomes multicellular, the 

 original Infusorian mouth becoming the mouth of the 

 multicellular animal, and the contractile vacuole its 

 excretory system. This theory, however, has not been 

 receiv^ed with any degree of favor, inasmuch as it lacks 

 confirmation from the developmental phenomena of the 

 Metazoa, the cases in which the segmentation results in 

 a syncytium (Crustacea, Insecta) being evidently a 

 secondary modification due to the accumulation of food- 

 yolk. There can be little doubt but that the segmenta- 

 tion of the ovum and the resulting formation of a 

 morula or blastula are most readily comparable to the 

 development of a colonial protozoan, and the theories 

 based upon this idea are more worthy of consideration 

 than that advanced by von Ihering. 



The first of these theories in point of time, and the 

 one which has had the greatest influence upon embryo- 

 logical investigation, is Haeckel's well-known Gastraea 

 theory. This made its appearance in 1872, and was the 

 outcome of the researches embodied in the classic " Mono- 

 graph of the Calcareous Sponges." The simplicity of 

 structure of the lowest calcareous sponges, and their 

 apparent similarity to the gastrula of the higher forms, 

 a similarity all the greater to the mind of Haeckel on 

 account of his erroneous conception of the structure of 



1 H. von Ihering. Vergl. Anatomic des Nervensystems und Phylogenie 

 der Mollusken. Leipzig. 1877. 



