135 
Bibliographical Notices. 
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, 
or more. Thus are formed as many nodes or articulations of the 
stem. 
“ Prolongation of the stalk seems combined with the evolution of 
the h)^dra by one of the few invariable laws ascertained. But the 
irregular duration of the successive hydree 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 v/here the 
head flourishes merely to decay. The utmost dimensions of this 
product are therefore as uncertain as the number of regenerated 
hydrse 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 Tuhularia indivisa 
(p. 22), but he has seen it, and described with great accuracy its 
phsenomena, in the Tub. ramosa, pp. 65 and 69. Thus the discoveries 
of successive observers wdll probabl)’’ prove the circulation of a fluid 
in the stems to be a general law in the physiolog}^ of these zoophytes, 
for negative observations cannot be allowed to invalidate the positive 
results olitained 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. Tuhularia larynx. This is very interestingly described and 
illustrated. 
3. Tuhularia 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 
