320 
Z. ASCIDIOIDA. 
Alcyonella. 
cies of Plumatella. Thus matters stood when Raspail was led, in 
1826 and 1827, to examine the subject, and the result of his inge- 
nious labours has been very curious, though some of his conclusions, 
notwithstanding the boldness of their enunciation, seem to me un- 
proved, and one of them, which identifies the Cristatella with the 
Alcyonella, has already been shewn to be erroneous. He has, how- 
ever, demonstrated very satisfactorily the entire sameness of the Po- 
lypes a panaches of Trembley, the Bell-flower animal of Baker, and 
the Alcyonella of Lamarck, — the variations in the polypidom, which 
had deceived all others, being produced by age, or by external and for- 
tuitous circumstances, as for example by peculiarities in its site : when 
this is the floating leaves of Lemnse, or the upper or under side of a 
stone, the developement is diffused, or lobed, or arborescent, or creep- 
ing, or massive and spongy, according as the polypidom has free- 
dom to spread, or is restrained by its position, or is influenced by the 
mere gravitation of one part against another. I can find, however, 
in the beautiful series of figures which illustrate his Memoir, none to 
make me assent to RaspaiFs opinion that all the Plumatellae are cer- 
tainly mere variations of this zoophyte : at present the facts appear 
rather of an opposite tendency ; — while, on the contrary, subsequent 
observations have shewn that he is right in considering as embryo 
Alcyonellse the Leucophra heteroclita and Trichoda floccus of Mul- 
ler, as well perhaps as the Difflugia proteeiformis of Leclerc, although 
Ehrenberg declares against this conclusion. 
RaspaiFs description of the zoophyte is admirable, and is rendered 
peculiarly interesting from the generalizations in physiology which 
the author ever and anon boldly hazards on certainly a very narrow 
basis ; and the curious experiments detailed in it. He has fully re- 
cognized the merits of Trembley, and has confirmed his accuracy in 
most particulars ; he has explained the cause which led Trembley 
erroneously to ascribe a retractor muscle to the body, the appearance 
being the result of a fold or plait in the tunic in certains positions of 
the body ; he ascertained the position of the anus ; gave a complete 
view of the tentacular apparatus, and an inimitable anatomy of the ova, 
which we shall transcribe at least in part. The ova, he says, are in ge- 
neral one-third of a millimetre in their longest diameter. On each of 
the two parallel faces we distinguish a shield, a little convex, and of 
the same shape as the egg itself, surounded with a rim of the same co- 
lour and consistence. (Fig. 49, a .) In drying, these two faces approxi- 
mate and become concave, while the rim remains unaltered. A sec- 
tion perpendicular to the two faces shews that the rim has no com- 
munication with the shield, (Fig. 49, b.) ; that it is distended with a cel- 
