60 



Mr. L. Hogben. 



is sufficient to favour increased rapidity of cell-division and induce abnormal 

 and varying forms. 



4. Marine algae grown in a limited volume of water and a limited supply of 

 air in sunlight and full daylight fix both carbon and nitrogen rapidly into 

 organic compounds. The amount of nitrogen fixed exceeds many times the 

 total nitrogen originally present as ammonia, nitrite, or nitrate in the water. 

 Moreover, the small initial amounts of nitrogen present in these forms are 

 not decreased. It follows that the only available source is the free nitrogen 

 of the atmosphere. 



Studies on Synapsis. III.- — The Nuclear Organisation of the 

 Germ Cells in Libellula depressa. 

 By Lancelot Hogben. 



(Communicated by Prof. E. W. MacBride, F.R.S. Received October 15, 1920.) 



[Plates 4-7.] 



An impressive array of facts in support of the chromosome hypothesis has 

 been elucidated by the researches of cytologists during the past two decades ; 

 nevertheless the paucity of direct objective evidence for the integral con- 

 tinuity of the chromosomes through all stages of nuclear history still 

 presents a barrier to unqualified acceptance of its validity. Such knowledge 

 is not only essential to a convincing presentment of the chromosome hypo- 

 thesis : it has furthermore a very intimate bearing upon the interpretation of 

 synapsis. 



The earlier workers, following Flemming, interpreted the prophase and 

 telophase organisation of the nucleus as a continuous spireme : this notion 

 rapidly hardened into a dogma, which not only handicapped further inqiiiry 

 into the problem of the constitution of the resting nucleus, but proved to be 

 a source of much confusion respecting the significance of the events in the 

 meiotic phase. How far theory even succeeded in overriding fact may be illus- 

 trated sufficiently by a quotation from a paper that has exerted a powerful 

 influence on cytological theory.* In reference to the spermatogonial 

 prophases of Periplaneta, the authors state correctly, " the method of 

 chromosome formation here depicted presents nothing exactly comparable to 

 the long spireme thread which is figured in so many existing accounts of the 



* ' The Meiotic Phase in Animals and Plants.'. 



