Bibliographical Notices. 135 



near the base ; but the mode of growth of the stalk itself is more re- 

 markable still. The head of the polype falls off and this is followed 

 by an elongation of the fistular stalk, the point from which the elon- 

 gation started being distinctly marked by a circular stricture ; another 

 head is then produced and this again falls away, and again there is 

 an elongation of the stalk upwards ; and so on the growth proceeds 

 for several periods in succession. But the successive growths are 

 not regular either in time or in their lengths ; the periods and length 

 of the new prolongations being dependent on circumstances not yet 

 understood. There is something in this very curious, and we shall 

 better impress attention to it by the following extract : — " Some re- 

 markable facts attend renewal of the head ; and first, the prolonga- 

 tion of the stem seems absolutely dependent upon it. Having lost 

 its head, the stem to all appearance remains stationary, unless in the 

 wound closing ; but from the moment that the rising internal bud 

 reaches the vacant extremity in its integument, the neck, or that por- 

 tion sustaining the young hydra, visibly lengthens, and so continues, 

 until further prolongation is arrested by the separation and fall of 

 the regenerated parts. The wound cicatrizes again. If reproduc- 

 tion follow by another embryo rising within to issue from the sum- 

 mit, a new prolongation ensues also ; and so on with a third, a fourth, 



<r more. Thus are formed as many nodes or articulations of the 



tem. 



" Prolongation of the stalk seems combined with the evolution of 

 the hydra by one of the few invariable laws ascertained. But the 

 irregular duration of the successive hydra; or heads produces an irre- 

 gularity in the accessions to the length of the stalk. One shoot ex- 

 tending six or eight lines may be followed by another of only two 

 or three ; and the prolongation seems scarcely sensible where the 

 head flourishes merely to decay. The utmost dimensions of this 

 product are therefore as uncertain as the number of regenerated 

 hydraj whereby they are attained. Let it be always remembered 

 that the prolongation of the hydra's neck is the sole medium of ex- 

 tension of the stem." (pp. 6, 7.) 



Sir John Dalyell has not been able on many trials to discover the 

 circulation described by Lister in the stalk of Tubularia indivisa 

 (p. 22), but he has seen it, and described with great accuracy its 

 pha;nomena, in the Tub. ratnosa, pp. 65 and 69. Thus the discoveries 

 of successive observers will probably prove the circulation of a fluid 

 in the stems to be a general law in the physiology of these zoophytes, 

 for negative observations cannot be allowed to invalidate the positive 

 results ol)tained by previous naturalists. How many have in vain 

 tried to see the currents in the living sponge ; and yet there is no 

 fact better ascertained than the existence of these currents ! 



2. Tubularia larynx. ITiis is very interestingly described and 

 illustrated. 



3. Tubulai'ia ramea. " This," says our enthusiastic author, " is a 

 splendid animal production — one of the most singular, beautiful and 

 interesting among the boundless works of Nature. Sometimes it 

 resembles an aged tree, blighted amidst the war of the elements, or 



