254 THE JOURNAL OP BOTANY 



descent. A fossil Diatom from the freshwater deposit of Monmouth, 

 in the American State of Maine, lying approximately at the latitude 

 of the Gi'eat Canadian Lakes — this deposit probably dating from 

 before the Glacial periods, — may be considered as the primordial 

 ancestral form from which the whole series was derived during the 

 post-glacial ages. This parental form is Navicula ononniouthiana 

 forma genuina. The gi'ouping together into lines of genealogical 

 descent closely connected intermediate foi'ms of Diatoms, which, in 

 the enormously crowded systematies of JJiatomacem, may otherwise 

 stand rather far apart, has been hinted at by Cleve. The present 

 attempt at what may be called synthetic integration of intermediate 

 forms has been undertaken in further pursuance of Cleve's idea. The 

 work mainly consisted in finding, between firmly-defined species, the 

 connecting links. The exhibited forms came from two European 

 and two American localities. They are all freshwater Some ai-e 

 firmly established species, others intermediate forms, which may be 

 given so-called hyphenated nominations, stating the initial species 

 from w^hich they seem to start and the final species to which they 

 seem to tend. The slides were shown in the following sequence, 

 corresponding to the line of their evolutionary descent : — Navictila 

 monmouthiana forma genuina, American fossil ; N. monmoutliiana, 

 witli first slight variation, towards the Sfodderi form, American 

 fossil; JSf. monmouthiana-Stodderi, an American living hyphenated 

 form ; Oymhella Stodderi, American living ; C. Sfodderi-angustata, 

 American living ; C. cequalis, European living ; C. angnstata, 

 European living ; Encyonema gracilis, American fossil ; E. scotica, 

 Eui'opean living; Gymhella d el icattil a, J^uroYie'An living; also living 

 in America ; C. gracilis-Cesafii, an American living — a hyphenated 

 form ; C. Cesatii, European living ; C microcepliala^ Euro])ean 

 living. The detailed examination of the above evolutionar}- ladder 

 suggests the hypothesis that the large, simple, and homogeneous 

 ancestral form Navicula monmoutliiana was a primordial species 

 adapted to the more uniform conditions of life on the planet during 

 the pre-glacial epochs, and that the Gymbellae which subseqviently 

 evolved from it are smaller, more complex heterogeneous forms, 

 gradually derived from Navicula monmoutliiana under the influence 

 of quite different and more varied conditions of life and climale, 

 which established themselves on the earth after the Glacial epochs, 

 at least luider the latitudes between 40 and tJO degrees North. A 

 similar trend of changes from larger and less varied foniis to smaller 

 heterogeneous ones has affected the whole of organic life after the 

 glacial extensions towards the South. No wonder that the same 

 trend has wrought similar changes also in Diatoms. Several authors 

 admit that the Cymhellce are degenerated Noi-iciilce. This seems 

 plausible, only the term " degenerated " can hardly be used as we 

 cannot know the direction of Evolution as a whole. The most we 

 can say is, that the immediate result of evolutionary changes consists 

 in a better adaptation, in the struggle for existence, to changed 

 conditions of life. 



At the same meeting, Mr. E. J. Collins read a communication on 

 *' Sex-segregation in the Bryophyta," of which the following is an 



