

PREFACE. xi 



MUELLEB'S Archiv, 1839, PP- 8 3 8 9> LAURENT Recherches sur I'Hydre el 

 VEponge d'eau douce, Paris, 8vo, av. Atl. fol. (1844), N. LIEBERKUEHN Eel- 

 trage zur Enticickdungsgeschichte der Spongitten in MUELLER'S Archiv, 1856, 

 B. 399 414, s. 496 514, CARTER on Spongilla in Ann. and Mag. of Nat. 

 Hist. 2nd Ser., xvni. p. -242, and ibid. XX. p. 21 and foil. 



To the works on the Rhizapoda, cited Vol. I. p. 47, may be added by 

 MAX SCHULTZE Beobachtung ueber die Fortpflanzung der Polythalamien in 

 MUELLER'S Archiv, 1856, pp. 165 173, from which it appears probable 

 that the shell of the young animal is formed within the body of the mother; 

 and by CARPENTER Researches on the Foraminifera in Phil. Trans. 1856, 

 I. pp. 181 236. 



The Hydra-form polyps are placed by LEUCKART in nearer 

 relation to the Acalephs under the name of Hydrasmedusce ; but the 

 great affinity between these animals had already been noticed by 

 VAN DER HOEVEN at p. 70 of the first volume : " It is possible that 

 all hydra-form polyps may be only imperfect forms of Medusce. ... At 

 all events the perfect form of Hydra would then be unknown." 

 Amongst the sea-nettles (Acalephce) most of the important disquisi- 

 tions of LEUCKART, VOGT and others, shewing that the Siphono- 

 phorce are compound organic bodies (as had already at a previous 

 period been the opinion of DELLE CHIAJE and MILNE EDWARDS 

 respecting some of them), were duly related at p. 102 and foil. So 

 also in the class of the Echinoderms, the investigations on the 

 metamorphosis by Prof. JOH. MUELLER up to the date of the Eng- 

 lish translation were supplied by the translator, pp. 137, 138. To 

 the memoirs of MUELLER, cited p. 138, must now be added another, 

 Ueber die Gattungen der Seeigellarven. Siebente Abhandlung ueber 

 die Metamorphose der Echinodermen. Mit 9 Kupfert. Berlin, 1855 

 (Konigl. Ahad. der Wissensch. zu Berlin, Jahrgang 1854). 



One of the most questionable points in the classification of in- 

 vertebrate animals is the true position of Bryozoa (called also by 

 Prof. ALLMAN and other, chiefly English, Naturalists, after THOMP- 

 SON, Polyzoa}. LEUCKART seems to hesitate whether they belong 

 to the worms in the vicinity of the Eotatoria or to the molluscs. 

 It seems indeed better to form of them a separate class, and not to 

 unite them to the Polyps. If, however, this class be placed near the 

 Tunicata in the great type of the Mollusca, in that case as many 

 objections might be urged 1 as are now advanced by different writers 

 against their union with the anthozoic type. There must always be 



1 See OWEN Lectures, &c. sec, edit. I. p. 154. 



