506 Royal Society. 



The Pyrosomata increase by gemmation also, but the gemmae are 

 solitary and do not form chains, becoming developed like those of 

 the ordinary compound Ascidians between tiie pre-existing forms. 



In the next section, the zoological relations of the SalpcB and 

 Pyrosomata, with the other Ascidians, are inquired into. The au- 

 thor endeavours to show that there is no essential difference of or- 

 ganization between the ordinary Ascidians and the Safpce, that the 

 two forms grade insensibly one into the other, and that there is, 

 tiierefore, no ground for breaking up the great ascidian family into 

 the two subdivisions of Monochitonida and Dichitoiiida. 



With regard to the theory of the " alternation of generations," 

 the author submits that it is by no means a proper expression for 

 the phaenomena presented by the Salpce. According to the author's 

 view, the two forms of Salpa are not two generations of distinct in- 

 dividuals, but are, properly speaking, organs, and only when taken 

 together, equivalent to an individual, in the sense in which that 

 term is used among the higher animals. 



For these pseudo-individuals, in this and all analogous cases, the 

 author proposes the name of " zooids," simply for the purpose of 

 avoiding the apparent paradox of calling these highly-organized in- 

 dependent forms " organs" though such, in the author's opinion, 

 they really are. 



The following letter, addressed to S. Hunter Christie, Esq., Sec. 

 R.S., by James Glaisher, Esq., " On the Extraordinary Fall of 

 Rain in the neighbourhood of London on the 15th instant," was 

 read. 



"13 Dartmouth Terrace, Blackheath. 

 1851, March 27. 



" My dear Sir, — The fall of rain in the neighbourhood of 

 London on the 15th instant was so remarkable, that 1 think an ac- 

 count of it will be interesting to the Fellows of the Royal Society. 



" At Greenwich it commenced falling about 1 o'clock a.m., and 

 by 9*^ A.M. the amount fallen was 1 inch, and by 4 o'clock p.m. at 

 the Royal Observatory 1'45 inch was measured ; at Lewisham the 

 fall was r725 inch ; in London an inch nearly had fallen by 9*" a.m., 

 and by ^^ p.m. the amount collected was 1*25 inch. 



"These quantities are unusual at any season, but particularly so 

 in the month of March ; there is no record either in the MSS. of 

 the Royal Observatory, or in the Philosophical Transactions, of so 

 large a fall in any day in the month of March, and, so far as I can 

 find, it is unprecedently large. 



'• The annexed table shows the amount of rain fallen on this day 

 at various places in England and Ireland. 



