150 



Messrs. G. C. and P. F. Frankland. 



[Mar. 3, 



possible on the application of tlie stimuli afforded by particular 

 surroundings; secondly, that some larvee, in the absence of these 

 stimuli, but in conditions otherwise favourable, are highly variable ; 

 thirdly, that the variations produced by a given change in the environ- 

 ment may be of an uniform and definite character ; and lastly, that 

 these changes may result, not in the modification of ancestral organs, 

 but in the hypertrophy of those which are purely larval. 



The last of these considerations leads to the hope that a further 

 investigation of similar cases may afford a criterion by which to 

 interpret larval histories in general. 



EXPLANATION OF THE FIGURES. 



Fig. 1. — Lateral longitudinal section (nearly median) through a young Bernini larva, 



just before the appearance of the collar-fold. 

 Fig. 2. — Transverse section through the trunk of a Bernini larva, at the time of the 



greatest development of the gilhpouches. 

 Fig. 3. — Nearly median longitudinal section through a degenerate Bernini larva. 



The arrangement of the tentaculiferous grooves is indicated by shading 



within the dotted lines. 

 Reference Letters. — An., anus ; Bl., blastocoel ; Br., branchial pouch; Ch., "noto- 



chord " of Bateson ; Ci., cilia ; GL, proboscis gland ; M., mouth ; Mc, 



"mesenchym" of proboscis cavity; P., proboscis pore; Ph.?, cells of 



blastocoel, possibly phagocytes ; Sch., " scheitelplatte " ; E, II, III, body 



cavities of proboscis, collar, and trunk respectively. 



II. " Studies of some New Micro-organisms obtained from Air." 

 By (Jr. C. Frankland, and Percy F. Frankland, Ph.D., 

 B.Sc. (Lond.), F.C.S., F.I.C. Communicated by E. Kay 

 Lankester, M.A., F.R.S., Professor of Zoology, University 

 College, London. Received February 15. 1887. 



(Abstract.) 



In previous communications to the Royal Society by one of the 

 authors,* details have been given of a number of experiments on the 

 presence of micro-organisms in the atmosphere. In these investiga- 

 tions a solid culture medium was employed, which not only greatly 

 facilitated their enumeration, but also presented them in an isolated 

 condition. In this manner the authors have met with a number of 



* 1. " The Distribution of Micro-organisms in Air," ' Roy. Soc. Proc./ vol. 40, 

 p. 509; 2. " A New Method for the Quantitative Estimation of the Micro- 

 organisms present in the Atmosphere," ibid., vol. 41, p. 443 ; 3. " Further Experi- 

 ments on the Distribution of Micro-organisms in Air by Hesse's method," ibid., 

 p. 446. 



