846 MICROSCOPIC FORMS OF ANIMAL LIFE 



several times a fine sand with foraminiferal and other shells will be 

 obtained. This can be then dried and sifted in the manner already 

 described for the sands from modern deposits. To insure obtaining 

 the minutest shells, the water which is poured off should be passed 

 through a fine cambric or silken sieve. 



The following are some of the more productive of the fossiliferous 

 deposits : 



Weathered surfaces of carboniferous limestone and seams of clay 

 in the joints of it. 



Clay from the lias formation. 



Gault clay especially from the upper zones. 



The softer beds of the upper chalk and especially the phosphatic 

 chalk of Taplow. which washes down easily. 



Foraminifera may be fixed by gum arabic with three drops of 

 glycerine added to the ounce, or with gum tragacanth, which has the 

 advantage of drying with a dead surface. 



SECTION II. RADIOLARIA. 



It has been shown that one series of forms belonging to the 

 rhizopod type is characterised by the radiating arrangement of their 

 rod-like pseudopodia, suggesting the designation Heliozoa or * sun- 

 animalcules ; ' and that even among those fresh-water forms that do 

 not depart widely from the common Actinophrys there are some 

 whose bodies are inclosed in a complete silicious skeleton. Now 

 just as the reticularian type of rhizopod life culminates in the marine 

 calcareous-shelled Foraminifera, so does the heliozoic type seem to 

 culminate in the marine Radiolaria; which, living for the most 

 part near the surface of the ocean, form silicious skeletons (often of 

 marvellous symmetry and beauty) that fall to the bottom on the 

 death of the animals that produced them, and may remain unchanged, 

 like those of the diatoms, through unlimited periods of time. Some 

 of these skeletons, mingled with those of diatoms, had been detected 

 by Professor Ehrenberg in the midst of various deposits of foramini- 

 feral origin, such as the calcareous Tertiaries of Sicily and Greece, 

 and of Oran in Africa; and he established for them the group of 

 Polycystina, to which he was able also to refer a beautiful series of 

 forms making up nearly the whole of a silicious sandstone prevail- 

 ing through an extensive district in the island of Barbadoes (fig. 644). 

 Nothing, however, was known of the nature of the animals that 

 formed them until they were discovered and studied in the living state 

 by Professor J. Miiller, 1 who established the group of Radiolaria, 

 including therein, with the Polycystina of Ehrenberg, the Acantho- 

 metrina first recognised by himself, and the Thalassicolla which had 

 been dis3overed by Professor Huxley. Not long afterwards appeared 

 the magnificent and ' epoch-making ' work of Professor Haeckel ; 2 



1 'Ueber die Thalassicollen, Polycystinen, und Acantliometren des Mittel- 

 meeres,' in Abhandlungen der Jconigl. Akad. der Wissensch. zu Berlin, 1858, and 



separately published ; also ' Ueber die im Hafen von Messina beobachteten Poly- 

 cystinen,' in the Monatsberichte of the Berlin Academy for 1855, pp. 671-676. 



2 Die Badiolarien (Rhizopoda Kadiaria), Berlin, 1862. This great work has 

 lately been followed by a gigantic monograph published in the c Challenger 'Reports, 



