TRANSACTIONS OF THE SECTIONS. 113 



of the Phanerogamia, associated with the vessels in the same fasciculus or layer ; 

 nor are thev ever surrounded by a stratum of cambium tissue ; but they are merely 

 indurated and transformed portions of the general parenchyma, and this even when, 

 as in some species, they form a sort of outer sheath to the fasciculi. Its great 

 variability is another point which assimilates this element rather to such sclero- 

 genous formations of the higher plants as nut-shells and other husky tissues, than 

 to the proper wood of their stems. In some it occurs only as a thin cortical coating 

 (Polypodium, Lastrea Filix-Mas, Asplenium Filix-Famina) ; in others it constitutes 

 the entire mass of the rhizome, except a thin sheath of soft tissue surrounding the 

 vascular bundles (Bleehnum, Osmunda, Hymenophyllum) ; while there are various 

 intermediate forms in which it occurs in the guise of isolated nodules or filaments 

 (Lastrea di/ufufu, L. oreqpteris) of sheaths to the vascular bundles (Asplenium), or of 

 one or more longitudinal tracts (AUosorus, Pteris). [These variations were illus- 

 trated by magnified sectional views of thirteen specie3, mostly British.] 



The true homologue of the stem-wood of the Phancrogamia is to be sought, it 

 has been suggested, in a fibrous stratum which occurs in the fasciculi of some tree 

 ferns, immediately within the cambium layer; far though these fibres have nothing 

 of a woody character, and are mostly represented in our indigenous species only by 

 an outer series of small and imperfectly developed scalariform vessels, it is the 

 outer layer corresponding to them which is woody in the fasciculi of the endogenous 

 stem, and in all the cases its development seems to show that it arises from a 

 peculiar transformation of the cells of the cambium tissue. 



Zoology. 



On the Acclimatization of Animals, Birds, fyc, in the United Kingdom. 

 By Frank T. Buckland. 



Remarks on the Respiration of the Nudibranchiate Mollusca. By Cuthbert 

 Collingwood, M.B., F.L.S., SfC, Professor of Animal Physiology in 

 Queen's College, Liverpool. 



The author described and exhibited drawings of a remarkable immature form 

 of Triopa claviger, which had led to the observations he was about to make, 

 moro especially on account of the entire absence of the branchial plumes. He 

 canvassed the Various definitions given by authors of the term Nudibranchiata, 

 and showed that, although it might with accuracy be applied to the family Pori- 

 dida?, the ^Eolididse could not with propriety be called Nudibranchs, inasmuch as 

 their papillae were neither anatomically nor morphologically to be regarded as 

 gills. These mollusks all respired by the whole surface of the body, more or less; 

 and the author suggested that in the Doridinse the appendages to the body were 

 supplementary to the branchial plumes; which, as a rule, were less developed in 

 them than iii the true Djrid.s, which were without such appendages. The fact, 

 however, that there was no specialized apparatus for respiration in the vEolidida?, 

 coupled with many analogies which that family bore to animals much lower in 

 the scale of organization, seemed to separate them much more widely from the 

 Nudibranchiata proper than was generally allowed. 



On the Nudibranchiate Mollusca of the Mersey and Dee. By Cuthbert 

 Collingwood, M.B., F.L.S., $c, Professor of Animal Physiology in 

 Queen's College, Liverpool. 



The author dwelt particularly upon the richnes3 of the estuaries of these 

 rivers in this beautiful group, and especially referred to some very interesting 

 forms, such a3 Doris depressa, D. suhquadrata, D. proxima, and Eohs Landsbwgii, 

 E. concinna, &c, which were found in them. The most interesting of all, however, 

 was Antiopa hyalina, a very local species, only found at Hilbre Island, in the Dee, 



1860. 8 



