THE HELIOZOA. 563 



of a nucleus, and the recent investigations of Schulze ^ and 

 Hertwig ^ have justified my hesitation. These observers have, 

 in fact, demonstrated the existence of one or more nuclei in 

 many Foraminifera (Entosalenia, Folystomella^ Rotalia^ 

 Texiularla., some Miliolldm). These nuclei may be simple 

 or multiple ; in the latter case, they have no special relation 

 to the cameration of the skeleton, and they are single in the 

 young. 



The discovery of the nuclei was effected by treating the 

 Foraminifera in which they were found in a special manner; 

 and, considering the negative results at which the best ob- 

 servers of the Foraminifera have hitherto arrived, and the 

 fact that the other Monera have not been investigated by 

 the same methods, it will probably be wise to consider the 

 question of the nonexistence of a nucleus in them as an open 

 one. 



Hertwig proposes to include all the Rhizopods which are 

 invested by a coat of chitin, or by siliceous or arenaceous par- 

 ticles, or which possess a skeleton, under the head of Thala- 

 mophora ; but the name of Foraminifera is now so widely 

 accepted and so long established that I cannot but think that 

 the better course is to retain it. 



I have included the Actinopliryida, and the similar forms 

 found in fresh water, and provided with Radiolarian skele- 

 tons, with the marine Radiolaria, 



Hertwig and Lesser,' however, in their important mono- 

 graph upon the Rhizopods, have stated reasons for separating 

 the former as a distinct group (the Heliozoa of Haeckel), 

 though their conclusion that there are, at present, no grounds 

 for assuming even a remote relation between the Heliozoa 

 and the Radiolaria [1. c, p. 159) appears to me to have no 

 sufficient warranty. 



The Heliozoa are defined by these authors to be unicellu- 

 lar organisms, which occasionally become multicellular, or at 

 any rate multinucleate, by the multiplication of the nucleus. 

 They are usually spheroidal and free, but some are fixed by 

 means of a stalk. In most, the protoplasm of which they con- 



1 " Khizopoden-Studien, VI." (" Arcliiv fur Mikr. Anatomie," 1876.) 



2 " Bemerkunffen zur Or2:anisation imd systematisclien Stelluiig der Forami- 

 niferen." {Jenaische Zeitachrift^ 1876.) 



3 '' Ueber Ehizopoden und denselben naliestehenden Oraranismen." (" Ar- 

 chiv fur Mikr. Anat.," Bd. x., Supplementheft, 1866.) Full references to the 

 literature of the subject will be found in this memoir and in Dr. Carpenter's 

 " Introduction to the Study of the Foraminifera," 1862. 



