1888-89.] Dr A. B. Griffiths on the Presence of Uric Acid. 135 
of animal life we have all the necessary “ mechanism ” for the 
organisms to breathe, digest, and excrete. The only difference is 
that in the Protozoa the cell performs numerous functions, whereas 
in the Vertebrata these functions are localised in special organs. 
Having in my studies on the physiology of the Invertebrata 
proved the renal functions of many doubtful organs, it would he 
interesting at this point to give, by means of a table, the physio- 
logical development of the renal system from the Protozoa to Mol- 
lusca. 
It will he seen from the above table that the primitive “kidney ” 
was a simple cell performing other functions besides that of a renal 
organ. In the next progressive stage of its development, we find 
the kidney, a cellular tubule secreting only waste nitrogenous matters 
and assuming a definite function. And, finally, in the higher stages 
of the Invertebrata the kidney becomes a sacculated and glandular 
organ resembling more in detail the vertebrate kidney. 
To conclude in the words of Professor Huxley : — “ In the 
Vertebrata ;, the renal apparatus is constructed on the same principle 
[as the renal organs of the Mollusca ] The vertebrate kid- 
ney is an extreme modification of an organ of the Annelid ; and, 
to go still lower, in the water-vascular system of the Turbellarian. 
And this, in its lowest form, is so similar to the more complex con- 
ditions of the contractile vacuole of a Protozoon, that it is hardly 
straining analogy too far to regard the latter as the primary form of 
uropoietic as well as of internal respiratory apparatus ” (The Anatomy 
of Invertebrate d Animals , p. 62). 
On Improvements in the Apparatus for Counting the 
Dust Particles in the Atmosphere. By John Aitken, 
Esq., Darroch. (With four Plates.) 
Part I. 
(Read February 4, 1889.) 
In a previous communication I described the apparatus first 
used for counting the dust particles in the atmosphere. That 
apparatus was constructed of such materials as could be easily 
obtained ready made, and was fitted together in such a way that 
any one acquainted with laboratory work could easily repeat the 
