THE OPALINID CELIATE INFUSORIANS. 447 



in the past been present in both Arctic and Antarctic regions whose 

 climate now precludes the residence of Anura: 7, That the genus 

 Zelleriella arose late in Patagonia and has spread a little into Aus- 

 tralia, and that it spread into tropical America after its union with 

 Patagonia : 8, That the genus Ce-pedea probably arose in the eastern 

 hemisphere and migrated to America, possibly by way of Siberia and 

 Alaska, but more probably both by this route and by a direct land- 

 bi'idge between Africa and eastern Brazil: That Cepedea did not 

 come to America from Africa via Antarctica: 9, That the genus 

 Opalina is probably a polyphyletic genus and may have arisen in 

 both the eastern and western hemispheres. [Further consideration 

 (1922) makes me accept the genus Opalina as of eastern origin, but 

 still leaves the likelihood that it is polyphyletic, Opalina virgula be- 

 ing of independent derivation from other species of the genus.] : 10, 

 That some eastern Opalinae have migrated to America : 11, That one 

 American Opalina has migrated by way of Alaska and Siberia to 

 Asia and across Europe to France: 12, That the multinucleated 

 Opalinids {Cepedea and O patina) entered South America from the 

 north or east and are still scarce in southern South America. [Error; 

 Opalina is unknown from South America]. 



Metcalf (1921,&) gives an abstract of a second paper read before 

 the same meeting of the American Society of Zoologists, as follows : 



A comparison of the geographical distribution of the species of 

 Anura with that of the Anuran Opalinids gives indication of the 

 following relations : 1, Patagonia was once connected with Australia, 

 doubtless by way of Antarctica, and at that time climatic conditions 

 in Antarctica were favorable for Anuran life. 2, At this time, 

 when Patagonia and Australia were united, Patagonia was not 

 connected with tropical America. 3, When Patagonia lost its con- 

 nection with Australia it established connection with tropical 

 America. 4, At a period later than the establishment of connection 

 between Patagonia and tropical America, the West Indian land was 

 still united to tropical America. 5, At a period at least as late 

 as this there was land connection between Siberia and Alaska and 

 a mild climate suitable for Anura. 6, For at least two geologic 

 periods there has been, as now, a bar to the migration of moist- 

 skinned Anura (Eanids and Leptodactylids) across northern 

 Mexico and southwestern United States. 7, There are four lines 

 of evidence from the Opalinids, but not conclusive, of a connec- 

 tion between Africa and tropical America .(not including Pata- 

 gonia). This land bridge was not by way of Antarctica. 



Hegner and Hsiang-Fong Wu (i921) report findings as to the 

 relation between growth and nuclear division in Opalina {larvai^rri] . 

 In young individuals with four nuclei " an increase of mass of body 

 per nucleus, represented by an increase in area [measured from 



