350 SUMMARY OF CURRENT RESEARCHES RELATING TO 



animal series, the same position in the body, and the same local 

 relations to the vascular centre and the alimentary canal." The fore- 

 most portion in Arthropods is simply displaced by the course of the 

 gullet in order to open by a mouth on the neural aspect of the body. 

 Where, as in Vertebrates, there is no oesophageal obstacle, the main 

 cerebral centres become more closely approximated. In fact, the 

 diflPerence between the central nervous system of Vertebrates and 

 Invertebrates is to be found in the " altered relation thereto of the 

 gullet and mouth." 



B. INVERTEBRATA. 



Apparently New Animal Type (Trichoplax adhaerens).* — Prof. 

 F. E. Schulze records the discovery of an animal quite different from 

 anything hitherto known. It was observed in the sea-water aquarium 

 of the Zoological Institute at Graz. It is a thin plate about 0*02 mm. 

 thick, and only a few millimetres in diameter. It constantly changes 

 its form. It is translucent, and greyish-white in colour. At rest it 

 is rounded in outline, but may draw itself out into a long thread, 

 which may so curl and twist that it recalls a Persian or a Turkish 

 letter. The movements are usually so slow as to be barely perceptible 

 as the animal creeps along upon its under surface. 



Microscopical examination shows that the whole surface of the 

 body is ciliated. Close under the upper surface is a layer of highly 

 refractile balls from 5 to 8 yut in diameter, and distributed pretty 

 evenly. Besides these there are other balls nearer the under surface, 

 which seem to be essentially different from those first mentioned. 

 There is no indication of internal organs, nor of only bilateral or 

 radiate symmetry : the organism is uniaxial. Schulze names it Tricho~ 

 plax (the ciliated plate), with the specific name adhoerens, because it 

 clings so closely to the surface on which it is moving. 



Such an organism one would expect to find related to the Protozoa ; 

 far from it, for two difierent epithelial layers of cells form its upper 

 and lower surfaces, and contain between them a fully developed layer 

 of connective tissue. The upper epithelium is composed of large, 

 flattened, polygonal cells ; the lower epithelium, on the contrary, is 

 composed of cylinder-cells, whose outer ends form a mosaic of small 

 polygons, but whose inner ends terminate in processes that are lost in 

 the connective tissue. This last, forming the middle layer of the 

 body, consists of spindle-shaped and branching nucleated cells, which 

 are probably contractile, and are imbedded in a hyaline basal sub- 

 stance. The balls above mentioned are contained in large cells. 

 There are, then, three layers, which from their relations would natu- 

 rally be compared with the ectoderm, mesoderm, and endoderm of 

 other metazoa : but the justification of this comparison must await a 

 knowledge of the development of the organism. 



Professor Schulze speculates as to the relationship of the creature, 

 but finds it impossible to assign it to any known class. Although it 

 has been watched for a year, no sign of metamorphosis or of repro- 



* 7jno\. Anzeig., vi. (1883) pp. 92-7 (2 figs.). 



