1907.] 



Rccor</s of the Indian Museum. 



49 



In all other respects, so far as its taxonomic features are con 

 cerned, the characters of the variety may be regarded as identical 

 with those of the typical form. 



F"i(;. I — Thick transverse section of the column of .1/ schillerianum var. exiil in 

 the region of the stomodpeum, showing the arrangement of the mesenteries, the form of 

 tiie retractor muscles and the muscular strands of the wall. 



Comparison between the Structure of the Typical 

 Form and that of the Variety. 



The above is a general account of the physical characters in 

 which the two forms agree with and differ from one another. In 

 order to explain the manner in which it is probable that these differ- 

 ences have come about , it will be necessary first to compare the 

 structure of the two forms in further detail, and then to give an ac- 

 count of their respective modes of life. 



Column. — 



The main differences between the typical form and variety are 

 ])lainly connected with the differences in the form of the column. In 

 the new variety of the species this part of the organism is a thin- 

 walled muscular sac with a bulky lumen ; in the typical form the walls 

 are thicker and the coelenteron very much less spacious. The thin- 

 ness of the walls in the variety is due to two causes, viz., the nature 

 of the ectodermal layer and the comparatively poor development of 

 the mesoderm. In both forms the ectodermal layer consists of the 

 usual elements, namely, epithelial and glandular cells, sense cells, 

 and nematocysts. The cells do not differ in any feature of import- 

 ance as regards form or structure from those found in the same layer 

 in other Actniians. vStolic/ka has already described and figured 



7 



