PT/ANIvTONRTTA ATLANTIPA. 141 



factory from every point of view. For sections, Delafielfl's 

 hasmatoxylin for three to six hours yields excellent results 

 alike for skeleton, ph^eodial corpuscles, and protoplasm. As 

 regards the skeleton, I failed to find anything which would 

 remove the phseodial corpuscles without also removing the 

 finer spines and meshwork, after tr3'ing various combinations 

 of organic and inorganic acids, alkalies, and pepto-hydro- 

 chloric digestion. HaeckeFs prescription, pure sulphuric 

 acid with a drop of fuming nitric at 60° C. for an hour or 

 two, yields beautifully clean preparations of the stronger 

 parts of the skeleton ; but the float, the lower part of the 

 shell, the finer spines, and the entire meshwork disappear 

 under its action. 



Summary. 



Planktonetta is a Phseodarian Radiolarian possessing in 

 addition to the ordinary shell of the Medusettidte a hollow 

 skeletal sphere, larger than the shell, here termed a float. 

 The body of the shell is of softer nature than its mouth. 

 The mouth of the shell carries eight spined arms, and gives 

 origin inwards to a skeletal meshwork across the aperture, 

 which serves to connect float and shell, and to support the 

 phaeodial complex. Between the mouth of the shell contain- 

 ing the extra-capsular protoplasm, and the body of the shell 

 containing the intra- capsular protoplasm, lies a fibrous dia- 

 phragm, which may be regarded as a part of the capsule. 

 The central capsule lines the body of the shell ; it contains 

 the nucleus and vacuolated protoplasm, the latter attached 

 by special processes, which perforate the capsule, to the dia- 

 phragm. A bundle of fine tubes leads from the intra-capsular 

 to the extra-capsular protoplasm, perforating capsule and 

 diaphragm. The extra-capsular protoplasm, permeated bj' 

 the skeletal meshwork, contains the phfeodial corpuscles of 

 various kinds in vacuoles. Of the structures here described 

 the float, the diaphragm, and the single bundle of tubes of 

 communication are unparalleled among Radiolaria. 



