EECENT EESEARCHES ON THE EADIOLAEIA. 157 



slight shock, while upon the return of tranquillity they resume 

 their expanded condition ; and Hertwig has not only found this 

 to be the case, but also that the external alveoli will close up and 

 disappear with the body's contraction. 



Very slight pressure also interrupts the flow of that protoplas- 

 mic current and granule circulation which normally exists. 



The pseudopodia are never drawn back within the capsule, as 

 is evident by the volume of the capsule remaining constantly the 

 same, though its form may change in some compound Eadiola- 

 rians. 



The animals are very delicate, and are mostly killed by the 

 mere act of catching them in a net. The Polycystine forms are 

 most often taken in a living state ; but the Acanthometrine forms 

 are generally dead when captured. In order to keep these ani- 

 mals any time alive, the water in which they are must be kept 

 pure and changed daily and considerable space must be allowed 

 to each animal. Haeckel found the Acanthometrine forms to be 

 the most sensitive and delicate, and these qualities to decrease 

 serially in the following groups : — (1) Splicer ozoida, (2) Collosphce- 

 rida, (3) Cladococcida, (4) Collida, (5) Ci/rtida, (6) Ethmosphcerida, 

 (7) Ommatida, (8) Spongida, and (9) Discida. 



The motions manifested by the Eadiolaria are like those shown 

 by the Polythalamia, but weaker, slower, and less obvious. Motion 

 seems to be confined to the extracapsular sarcode, though the 

 capsules of some compound species have been observed to change 

 their shape. The motions are produced by granule streams, as in 

 the Polythalamia. But these do not result in creeping movements 

 as in them, inasmuch as the Eadiolaria are essentially floating 

 organisms, and generally have their pseudopodia far extending on 

 all sides. It is a problem how they efiect this swimming motion, 

 since their specific gravity is greater than that of water. It is 

 possible they may overcome gravity by active motions of their 

 pseudopodia, or by expanding them distally at the surface of the 

 water so as to act as a sort of float. The contraction and expan- 

 sion of the alveoli would explain the rising and sinking of such 

 forms as Thalassicolla ; but, then, most Eadiolaria have no alveoli. 

 They can move on solid surfaces by successively contracting their 

 pseudopodia after adhesion, an action which has been observed by 

 Haeckel in his Collida, Cyrtida, Ommatida, and Discida. The 

 pseudopodia may ramify, then broaden out at their ends and apply 

 themselves to an object, over which the Eadiolarian rolls itself by 



