Mr. J. Ralfs on the Diatoraaceae. 447 



liquid parts doubtless the whole fabric of the body is renewed 

 or nourished. 



Now if the sacculi of the Polygastrica perform the same func- 

 tions, as regards the fluid in which they are suspended, as do the 

 suspended particles in the chyle and blood, where is the fluid in 

 which these sacculi are suspended ? It has certainly never been 

 demonstrated ; and the only experiment upon which such a \dew 

 can have been based, is that of the action of imbibition, and 

 which is undoubtedly an error. INloreover, were this view cor- 

 rect, the cavity of the animalcule would be that in which the 

 blood, so to speak, of the animalcules is contained ; and what a re- 

 markable anomaly would be the introduction of a large animalcule 

 into the cavity in which the blood is contained, as would undoubt- 

 edly be the case in the carnivorous Infusoria, were such a view 

 correct ! Again, foreign alimentary solids have been traced into 

 and detected in the sacculi ; but solid alimentaiy matters have 

 never been traced into, or detected within, the blood or chyle 

 globules. 



In conclusion we must remark, that all the phsenomena relating 

 to the digestion and circulation of the Polygastrica may be ex- 

 plained — 1. By the existence of an internal convoluted aliment- 

 ary canal, whose existence is made kno\\Ti to us by its con- 

 tents and the coiu-se they take. 2. These contents, sometimes 

 solid, sometimes fluid, or semifluid, distending different parts of 

 the canal, in which they are detained, produce the appearance of 

 vesicles or sacs, which have been denominated, and probably 

 perform the real ofiice of stomachs. 3. That the portions in 

 which the contents are delayed are not blind pouches leading 

 from a common tube seems positive, from the circular dii'ection 

 assumed by these contents, which indicate its dii-ection. 4. There 

 is, without doubt, a difi"erence in the length and dii-ection of the 

 alimentary tube in the Polygastrica as well as in other animal 

 beings, depending upon variations in the nature of then* food. 

 5. '^'VTien solution of potash is added to the liquid in which these 

 atoms exist, it dissolves the external tunic, and Liberates for a 

 short time its contents ; these are next partly dissolved, when 



LXII. — On the Diatomacese. By John Ralfs, Esq., M.R.C.S., 

 Penzance*. 



[With Plates.] 



Ox commencing the study of the Diatomacea I experienced con- 

 siderable diflicu.lty in determining several of my plants from the 

 descriptions in om* British works, and soon found that in this 



* Read before the Botanical Society of Edinburgh. 



