12 ZOOPHYTES. 



the whole product being white and very vigorous : the head fell in twenty- 

 one days from the first, leaving the stalk nearly four lines high. In seven 

 days it was suceeeded by a second, also pure white, but with only eight 

 tentacula. This subsisted eleven days, without acquiring the vigour of its 

 precursor :-^Plate III. fig. 40 ; enlarged, fig. 41, distinctly shewing the 

 ascent of the neck from within. In a recent instance the second head of 

 a nascent specimen was developed with six tentacula. 



Considerable difference is presented by the aspect of different nascent 

 animals from the cyst, and especially in the curvature of the stem, so sel- 

 dom straight, which may be influenced by the hardness and smoothness of 

 the glass, whereon in this artificial state it was founded throughout the 

 course of my observations. — Figs. 20-41. 



There are also considei'able disparities in the comparative dimensions 

 of the head with the rest of the product ; — as well as in the comparative 

 rates of increment of those which are fixed or free, — all resulting, per- 

 haps, from the pabulum afforded by their respective site. Of four nascent 

 tubularise, produced in April, two had seventeen tentacula, one fifteen, and 

 the other fourteen. The last never adhered, but it grew more rapidly, and 

 on losing its head, had extended half an inch, — exceeding the others, though 

 the head of one subsisted at least thirty days. 



Thus no undeviating rule is prevalent in determining the circum- 

 stances incident to the existence of the tubularia, although the necessary 

 conditions under which the race shall be preserved are governed by gene- 

 ral laws. 



Vigour is indicated by the number and size of the tentacula ; but the 

 delicacy of the product seems to preclude its preservation until the ruddy 

 tinge of maturity darkens the original white of the nascent tubularia. 



It may be questioned whether, according to the common course of 

 nature, the fall of the head should precede the expulsion of the foetus from 

 the cyst. From the evident accessions received by the stalk, indicating reno- 

 vation of the head, we may certainly conclude that this incident constantly 

 occurs to the product in its proper abode previous to removal from it. 



We collect from the preceding detail, that an external ovarium is 

 situated among the other parts composing the hydra or head of the Tubu- 

 laria indivisa ; — that the unusual recurvature of the tentacula, their irre- 



