RADIOL ARIA 



85 



the ivmaining Eadiolaria (Monocyttaria). They may either lack 

 a skeleton (Collozoidae, Fig. 22), or have a skeleton of detached 

 spicules (Sphaerozoidae), or possess latticed shells (Collosphaeridae) 

 (tue for each capsule, and would seem therefore to belong, as only 

 differentiated by their colonial habit, to the several groups having 

 tliese respective characters. Fission has been well studied in 

 Aulacantha (a Phaeodarian) by Borgert.^ He finds that in this 

 case the skeleton is divided between the daughter-cells, and the 

 missing part is regenerated. In cases where this is impossible 

 one of the daughter-cells retains the old skeleton, and the other 

 escapes as a bud to form a new 'skeleton. 



A B C 



Fi«;. 28.— Shells of Challengeridae : A, Tuscarora; B, Pharyngdla ; C, llaeckeliana. 

 (Frnni Wyville Thomson.) 



Two modes of reproduction by fiagellate zoospores lia"\'e been 

 described (Fig. 22). In the one mode all the zoospores are alike — 

 isospores — and frequently contain a crystal of proteid nature 

 as well as oil -globules. In the Polycyttaria alone has the 

 second mode of spore-formation been seen, and that in the same 

 species in which the formation of isospores occurs. Here 

 " anisospores " are formed, namely, large " mega-," and small 

 '■ micro - zoospores." They probably conjugate as male and 

 female respectively ; but neither has the process been observed, 

 nor has any product of such conjugation (zygote) been recognised. 

 In every case the formation of the zoospores only involves the 



^ Znnl. Jahrh. Anat. xiv. 1900, ]>. 203. 



