137 
Bibliograjihical Notices. 
time externally ; nor can it be forcibly removed without the visible 
reluctance of this diminutive being.” (pp. 144-5.) 
8. Sertularia ahietina. A monograph of interest equal to the pre- 
ceding. The figure on pi. 23 is an admirable portrait of the species. 
The species has “ two differently formed vesicles,” “ a fact also in- 
cident to a few other Sertularia'' One of the vesicles is ampullate 
or flask-shaped with nearly white contents and numerous oviform 
corpuscula ; the other is compound, “ the spherule containing a 
single yellow globular corpusculum,” p. 155. Here we are informed 
that “ great diversity occurs in the shape of the same planulse, from 
whatever zoophyte they come. Nothing can be more variable than 
their soft, extensile and contractile bodies, in motion or at rest ; and 
according to the freshness of their element or the temperature of the 
atmosphere, and especially when about to undergo the metamor- 
phosis incident to their race.” (pp. 155-6.) 
The following paragraph is also interesting : — “ The evolution of 
the nascent Sertularia, from vesicles in situ, is a rare occurrence. 
We have seen that, from some unnatural retention in the cysts of 
the Tuhularia, the organs of the young may begin to unfold. This 
may tend to corroborate and explain a figure given by Ellis, repre- 
senting a hydra issuing from a vesicle of the Sertularia pumila. But 
it is to be noted also that examples are not wanting of portions of the 
Sertularia vegetating through an empty vesicle with a generated or 
regenerated hydra. I can account for it only from the sudden me- 
tamorphosis frequently rendering the planule motionless, and thus 
precluding its escape from the vesicle. But although this may ensue 
in the Sertularia ahietina, the discharge of the planule from the ve- 
sicle, to undergo its metamorphosis unrestrained, is the ordinary and 
natural course whereby the species is perpetuated.” (p. 156.) 
9. Sertularia ahietinula. This is merely an early state of S. ar~ 
gentea, so far at least as fig. 7 of pi. 25 is concerned. Fig. 6 seems 
to represent a small specimen of S. ahietina. 
10. Sertularia rosacea. 
11. Sertularia pumila. We doubt whether figures 19 and 20 of 
plate 26 represent this species. 
12. Sertularia halecina and cognates. The natural-sized figures of 
this species are beautiful and correct, but drawn from small speci- 
mens. We differ from the author in referring Ellis’s S. halecina., as 
exhibited in pi. 10 of his ‘ Corallines,’ to Thoa Beanii ; it seems to 
us to be a good figure, and certainly not “ from an indifferent draw- 
ing,” of the true S. halecina. This is elaborately described by our 
author, but we cannot be brought to admit that Thoa halecina and 
T. Beanii are only states of one species, although the observations of 
Sir J. Dalyell shake our confidence in their absolute distinctness. 
The question is still open to future inquiry. 
The following quotation describing the rapid growth of the polypes 
is interesting ; — “ Where vigorous hydrse already subsist, the rege- 
neration of others advances in their vicinity — the clear and transpa- 
rent sheath showing their progressive evolution. Nothing can be 
more interesting than to witness the rapid refinement of an embryo 
