252 G. T. HARRIS ON THE 



been said that strong sunlight is inimical to the life of the Chloro- 

 phyceae (8) ; but the condition of this pool would hardly support 

 the statement, as a long spell of unclouded days had been experi- 

 enced. The Postbridge material was collected the latter part of 

 September and beginning of October 1916, and extremely advene 

 weather was experienced, the entire month spent there being 

 wet and windy and the bogs becoming so swollen and saturated 

 that it was almost impossible to get far into them. On this 

 account I do not consider that the enumeration of species, etc., 

 under this district in the census table quite fairly represents 

 the richness of the locality. The rivers and mountain streams of 

 Dartmoor were passed over entirely, as the bogs and moor pools 

 were too numerous to permit of time being devoted to them. 

 A test examination of the Dart at Postbridge (where it is a swift 

 mountain stream) was, however, made and from a small gather- 

 ing some fifty species and varieties were obtained, all common 

 to the bogs situated higher up the river, from which they most 

 probably came in periods of flushed streams. 



In connection with the dispersal of desmids I would refer to 

 the extent to which these plants are ingested by various forms 

 of aquatic life. Larvae seem frequently to ingest them, and 

 as I have noticed the desmid almost through the body of the 

 larva with its chloroplasts still apparently uninjured it would 

 seem that the secretions of the animal do not seriously affect the 

 vitality of the desmid. In one rotifer I counted two individuals 

 of Tetmemorus granulatus, two of Tetmcmorus Brehissonii var. 

 minor, two of Staurastrum functulatum and one of Staurastrum 

 dejectum. In one individual of a species of Euchlanis I counted 

 the following desmids : three individuals of Cosmarium Bre- 

 hissonii, two of Tetmemorus granulatus, one of Micrasterias denti- 

 culata, one of Tetmemorus Brehissonii^ one Euastrum ansatum, 

 one Cosmarium difficile, one Staurastrum functulatum, one 

 Cosmarium suhcrenatum and one of Tetmemorus Brehissonii var. 

 minor. In none of these as far as could be made out did there 

 appear to be any digestion of the chloroplasts proceeding. Pro- 

 fessor G. S. West suggests (9) that the armature of desmids has 

 been developed as a protection against aquatic enemies, and 

 while none of the species mentioned as having been ingested has 



