450 rnor. a. dendt on pontobolbos, 



in tlie ciliated embryo. Marshall has described * the occurrence 

 of an Oscillaria in Dysidea {Psavimoclema) ramosa, in which it 

 is noteworthy that he was unable to detect chlorophyll. 

 TracJiyeladus Icevispirulifer, again, a common Australian sponge, 

 according to Carter f owes its characteristic red colour to an 

 Oscillarian which has the form of short rods consisting of only 

 four cells each. 



Amongst the Protozoa, many Hadiolarians are habitually 

 infested with " yellow cells," now generally believed to be sym- 

 biotic Algae ; and, in short, the association of low forms of animal 

 and vegetable life in what is presumably a symbiotic manner is 

 a, phenomenon of common occurrence, while the parallel case of 

 the Lichens will occur to everyone. 



Assuming that Pontoholhos owes its origin to such symbiosis, 

 it is not difficult to see what mutual advantages would be derived 

 by the associated organisms. The Uhizopod gains an admirably 

 firm and tough skeleton of cellulose, and is thus relieved from 

 the necessity of secreting the usual calcareous skeleton. In 

 accordance with the law of economy in skeleton-formation the 

 latter may have disappeai^ed, though possibly the irregular 

 calcareous layers described above may represent the proper 

 skeleton in a vestigial condition. "With the proper skeleton, of 

 course, all traces of the chamber-arrangement, so characteristic 

 of the Eoraminifera, may be supposed to have disappeared also, 

 if indeed it ever existed. The Schizophyte, on the other hand, 

 being in all probability bacterial in nature and devoid of chloro- 

 phyll, may well be supposed to obtain its food-supply at the 

 expense of the Ehizopod. 



The chief objectiouB to the hypothesis of symbiosis in the case 

 of Pontoiolbos lie, first, in the failure, as noted above, to dbtain 

 the characteristic protoplasmic reactions with Millon's reagent 

 and with nitric acid and ammonia; and, second, in the failure to 

 detect nuclei in the supposed protoplasmic layers and network. 

 These objections appear to me at present to be very serious, 

 although it must be borne in mind that micro-chemical reactions 

 are not always conclusive, and that nuclei have not yet been 

 detected in all the known lower organisms, while the staining 

 with borax-carmine, aniline dyes, and iodine must also be 

 accounted for. All I have been able to do has been to describe 



* Zeit. wiss. ZooL, Ed. xxxv. p. 111. 



t Ann. & Mag. Nat. Hist. [5] xvi. p. 357. 



