90 NOTES AND OBSERVATIONS ON BOARD H.M.S. RATTLESNAKE 



The animal is an unchanged cell in Euglena, in Amoeba and in 

 Opalina. In others, as the Vorticellm, there is a more or less distinct 

 permanent cavity in the interior of the cell which opens externally, an 

 occurrence not without parallel among the secreting cells of insects. 

 Certain genera, such as Nassula, have an armature of spines, but so 

 have some of the Gregarinidse which are unquestionably simple cells. 



Contractile spaces, — cavities which appear and disappear in different 

 parts of the Infusoria, and sometimes become filled with theingesta, — 

 are found no less commonly in the component cells of the tissues of 

 many of the lower animals, and according to Cohn in the primordial 

 cells of plants also. 



The " Polygastria," then, may be justly considered to be simple 

 cells, and to form a type perfectly comparable with Thalassicolla. 



The researches of Henle, Stein, and Kolliker have made us 

 acquainted with another form of cellular animals — the Gregarinidee. 



These are nucleated cells, without cilia, but with contractile walls, 

 which lead an independent parasitic life in the intestines of many of 

 the Invertebrata, principally insects. 



The Gregarinid^e, like the Infusoria, are generally, if not invariably, 

 single, solitary cells. 



A third type is formed by the Foraminifera. The fate of these 

 animals is somewhat singular. Considered to be Cephalopoda by 

 D'Orbigny ; Bryozoa by Ehrenberg ; rudimentary Gasteropods by 

 Agassiz.; all careful observation tends to confirm the opinion of 

 Dujardin, that the fabrication of their remarkable shells is essentially 

 similar to Aimvba and Arcella, both of which have been shown to be 

 nucleated cells. 



Lastlj', we have the Sponges. That the tissue of the Sponges 

 breaks up into masses, each of which is similar to an Ain(Bba,\v&s been 

 pointed out by Dujardin, and confirmed by Carter and others. Du- 

 jardin, however, believing that a peculiar formless substance, " Bar- 

 code," constitutes the tissues of the Sponges (as well as of the Infusoria 

 and many other of the lower animals), fails to point out that they are 

 mere aggregations of true cells. 



This is not the place to discuss the important question, whether 

 the great law developed by Schwann does or does not hold good among 

 the «'hole of the lower animals. I believe that there is evidence to 

 show that it does ; that everywhere careful analysis will demonstrate 

 the nucleated cell to be the ultimate histological element of the animal 

 tissues ; and that the " sarcode " of Dujardin, and the " formless con- 

 tractile substance " of Ecker, are either cells or cell-contents, or the 

 results of the metamorphosis of cells. Be this as it may, however, I 



