Bibliographical Notices. 137 



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 planulae, 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 SertularicB, 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 froin. 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 abietina, 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 abietinula. This is merely an early state oi 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 



