2 Cerairia of Schiatofunnum Spindcdw (Montgomery).
into the j>()ssil)ility ui tlic sprcitd of liuniaii Billiaiziosis in India. At that time jjaiticuUir attention uas heini; ])aid to discoverinj; liunum .schistosome cercaria' in liiis country, and the tindini; of one which ])().•<- sessed the main characters of these cercaria' aroused considerable interest. At first it appeared that the new form foimd in Homliay was probably one of the human cercaria', but as no more detailed ile.scription of their structure beyond the main features given by Lei[)er was at that time available, identity of the present species with the human form could not be taken as established on superficial morphological .similarity alone. It was, therefore, proposed to settle this point experimentally b}' attempting to raise adult ]iarasites from the cercari.r, and comparing the structure of the mature adults with that of the schistosomes already known. For this after all is the only final test of the identity or otherwise of the larva' with the adult. Structural correlation between a known cercaria and one under investigation may at best be suggestive of their possible identity, but the final proof must rest with the experimental rearing from them of identical adults.
Of course, the experimental method too has many pitfalls and unless great care is taken the results are apt to be misleading. Indeed, as Cort(') observes 'in some very recent work, as well as in older papers, larva" and adults, shown later to be entirely unrelated, have been joined experimentally." But this only emphasises the great importance of care and proper controls in conducting such experiments.
It was deemed advisable not to give the cercariae any specific names — the cercaria being but a larva of the adult parasite — but to give them proT[sional numbers till such time as their life-history had been worked out, when they would naturally be named after the adults. Accordingly this cercaria was designated Cercaiw hottthui/ensis No.i.
Infection experiments were carried out which proved that this cercaria was not of a schistosome which affects human beings, but was of an animal infecting type — Scfiistosomutn spiiidali^. A brief account of these experiments has already been published in the Indian Journal of Medical Research.(-) The results have since been confirmed by repeated exjieriments, and there is now no doubt that this cercaiia forms the larval stage of Schislosomum spindolis (Montgomery). Life-histoi'v studies on furcocercous cercariae have been very meagre and this appears to l)e the first in.stance in which an animal .sfbistosome cercaria has been discovered and its life-history tracetl through the various stages of jt.^
