42 Prof. Mcintosh's Notes from the 



account of certain forms of Bougainvillia paradoxa from the 

 White Sea which were totally devoid of a manubrium, and 

 this was the more readily noticed from the absence of the 

 dark red coloration usually characterizing it. Careful search 

 for the manubrium revealed no trace, the whole gastro-vas- 

 cular system consisting of a circular and four radial canals, 

 without stomachal dilatation or communication with the exte- 

 rior. The endodermic cells of the canals showed active ciliary 

 motion, but no food could reach them. These specimens, 

 which had attained about half a centimetre, had therefore 

 reached nearly (but not quite) full size without being 

 nourished in the ordinary way. Another species belonging 

 to the same genus was occasionally found in a similar con- 

 dition, the four radial canals meeting without forming a 

 stomachal cavity and the mouth being entirely absent. 



Mereschkowsky considers it is clear that such Medusa} live, 

 and increase in size from a minute embryo without digestive 

 organs, and even apparently without nourishment. Yet the 

 latter notion cannot be accepted, and after searching through 

 all the possible means he comes to the conclusion that " the 

 Medusa can nourish itself by means of its ectoderm by 

 absorbing the organic material dissolved in the sea-water." 

 He cites the case of certain sponges which nourish themselves 

 upon organic matter dissolved in sea-water, and also by means 

 of their ectoderm, and thinks it possible that the Medusa can 

 dispense with its entoderm and yet live and attain nearly 

 its normal size. The ectoderm therefore in such cases fulfils 

 the function of the entoderm, i. e. extracts and assimilates 

 the organic matter dissolved in sea-water. He never found 

 solid particles on the surface of the Medusa, and he is of 

 opinion we have really to do only with organic matter dis- 

 solved in sea-water. 



The theory broached by Mereschkowsky is not altogether 

 new, but has formerly been brought forward to explain the 

 nourishment of marine animals. Thus the naturalists of the 

 1 Porcupine ' Expeditions of 1869 and 1870 held that the 

 marine Rhizopoda, like the Entozoa, had the power of absorb- 

 ing organic matter or " diffused protoplasm " in sea-water. 

 Moreover there is this feature in common with the abnormal 

 Medusas, viz. that both are devoid of a mouth. The same 

 views therefore would equally apply to both. As formerly 

 shown*, the question indeed is a wide one, and the remarkable 

 tenacity of life exhibited by certain marine animals confined 

 in pure sea- water lends some countenance to the notion. 



* Ann. & Mag. Nat. Hist. ser. 4, vol. ix. p. 1 (1872). 



