386 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



that these retained their distinctive characters for over 

 a year. 



It may well be, however, that in the constant 

 environment of a laboratory experiment a marked 

 variation or " form," arising as a mutation, 

 may continue to preserve its distinctive characters 

 through many generations and appear to be stable; 

 while under the varying conditions of a natural 

 life in the open sea such marked variations may arise in 

 some individuals, persist for a time, and then die out or 

 be replaced more or less completely by one of the other 

 forms. When examining a gathering such as we show 

 in fig. 3 (p. 381), the' forms a and b certainly seem very 

 distinct; but on the other hand, the figures we give on 

 PI. I, like the cases quoted from Gran (in Murray 

 and Hjort), do not seem explicable on the view that we 

 are dealing with independent species. They may be 

 regarded as mutations which under some circumstances 

 breed true, but sometimes throw back to the original 

 form of the species. 



EXPLANATION OF PLATE. 



Fig. 1. Biddulphia mob., f. sinensis, as it first appeared in the 



Irish Sea in 1909. 

 Fig. 2. Ditto, a slightly elongated form. 

 Fig. 3. Ditto, normal division as it appeared in 1910. 

 Fig. 4. Ditto, transition form in process of development. 

 Fig. 5. Ditto, transition form after division and elongation. 

 Fig. 6. Ditto, normal but rather slender form dividing. 

 Fig. 7. Ditto, one end without continuation processes. 

 Fig. 8. Ditto, the form ' ' sinensis-mobiliensis " dividing. 

 Fig. 9. Ditto, one end without continuation processes. 

 Fig. 10. Ditto, mobiliensis dividing. 

 Fig. 11. Ditto, slender but nearly normal form. 

 Fig. 12. Ditto, abnormal form. 

 Fig. 13. Ditto, probably a dead cell, showing divisions unusually 



near the end. 

 Fig. 14. Ditto, mobiliensis dividing. 

 Fig. 15. Ditto, mobiliensis dividing. 



Fig. 16. Biddulphia mobiliensis, " regia " form of long shape. 

 Fig. 17. Ditto, " regia " form of short shape (turned sideways). 

 Fig. 18. Ditto, " regia " form dividing. 

 Fig. 19. Ditto, " regia " form dividing. 



Fig. 20. Ditto, " regia " form approaching Ostenfeld's " mobiliensis." 

 Note the unusual number of spines in figs. 10, 12, 14 and 15. 

 The figures are all photographs of equal magnification. 



