THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[FOURTH SERIES.] 

 No. 46. OCTOBER 1871. 



XXVII. — Outline of a Scheme of Classification of the Inverte- 

 hrata, founded upon the Progressive-Development Theory. 

 By John Denis Macdonald, M.D., F.R.S., StafF-Surgeon 

 H.M.S.' Lord Warden'*. 



On studying the leading members of the Protozoa with the 

 view of discovering, if possible, their nearest descendants, the 

 whole subkingdom of Invertebrate animals arranged itself, 

 apparently quite naturally, into as many groups as there were 

 points of origin. In unfolding the results of this investiga- 

 tion, which must, of course, be more or less speculative, Prof. 

 Huxley's arrangement of the Protozoa may be taken as a 

 basis, thus — 



Protozoa. 



Astomata. Stomatoda. 



1. RHzopod type. 2. Gregarinidae. 3. Infusoria. 4. Noctilucidse. 



The four groups numbered in the above table exhibit a 

 marked increase in their vital activity and structural develop- 

 ment in the order in which they stand ; and although there is 

 no reason to doubt that the last three may have been derived 

 from the first, the upward evolutional tendencies of all would 

 appear to be quite distinct. Indeed each may be regarded as 

 primordial in its own series, or the salient point of descent 

 and divergences, which, however diflferent inter se, may be 

 referred to their own definite source. 



1. Tracing from the Rhizopod type to the simple polyps, 

 in fact, to the Coelenterata crowned with the Ctenophora, and 

 from the latter through the Brachiopoda and Polyzoa to the 



* Communicated by the Director General of the Medical Department 

 of the Navy. 



Ann. (So Mag. N. Hist. Ser. 4. Vol. viii. 17 



