288 PKOF. ALLMAN ON THE RECENT liESEAECUES 



only as inhabitants of the sea, has for some years been reward- 

 ing the researches of several investigators of the lower forms of life. . 



It is to be I'egretted, however, that their descriptions are in 

 many instances very contradictory, and often diflfer from one 

 another so much as to render it difficult to find in them grounds 

 for a satisfactory conclusion regarding the true structure of the 

 organism which forma the subject of investigation *. 



There can be no doubt, as has just been said, that the affinities 

 between these freshwater organisms and the true Eadiolaria have 

 been exaggerated. Hertwig and Lesser, in their valuable me- 

 moirf, already frequently referred to, enter fully into the question 

 of the relation between these Eadiolaria-like organisms and the 

 true Eadiolaria, and arrive at the conviction that there is no 

 close affinity between them, and that the proper allies of the fresh- 

 water forms are the long-known " sun-animalcules " Actinophrys 

 and ActinospTiceriwin, with which they accordingly associate them 

 in the natural group of the Heliozoa. 



In order to aid us in forming an accurate judgment on this 

 question, it may be well to bring together here the more important 

 characters of the true Eadiolaria. From the researches of Huxley, 

 and more especially of Johannes Miiller and of Haeckel,we are now 

 well acquainted with the structure of certain minute organisms 

 known to the popular observer chiefly by the beautiful little silice- 

 ous shells which Ehrenberg had described under the name oiPoly- 

 cystina, and which, with their allied forms, constitute a w^ell-defined 

 zoological group. To this group Miiller has assigned the name 

 of Badiolaria. It consists of minute, sarcodic, more or less sphe- 

 roidal organisms, which are usually provided with beautifully 

 symmetrical siliceous skeletons, either in the form of perforated 

 cases or of radiating spines, and whose body presents two concen- 

 tric zones, the inner separated from the outer by a chitinous capsule 

 ("central capsule "), and composed of numerous true nucleated 

 cells. In almost every instance peculiar cells are also found im- 

 bedded in the sarcode which forms the outer or extracapsular 

 zone. These cells contain a yellow pigment, and constitute the 

 so-called " yellow cells." 



* Since the reading of the present Address an excellent resume of recent re- 

 searches among the Heliozoa and other rhizopodal forms, with valuable critical 

 remarks, has been published by Mr. Archer. See ' Quart. Journ. of Micr. Sci. ' 

 for July and October 1876 and January 1877. 



t " Ueber Rhizopoden u. dcnselben nahestehende Organismen,"' Archiv f. 

 mikr. Anat., Band x. Suppl. Heft 1874. 



