16 i Mr. R. Q. Couch on the Morphology of Zoophytes. 



without a bulbous termination. The granular matter or pulp, 

 which is at first diffused, becomes condensed or organized to- 

 wards the centre, leaving the investing sheath in its annular 

 form, and no further development goes on. It is this cessation 

 of growth for the purposes of organization that regulates the 

 length of the internodes both of the trunk and branches. Hence 

 also arise many of the irregularities so frequently observed. If 

 growing in a variable situation, some of the internodes are short, 

 while others are nearly double the usual length, depending on 

 the vigour with which each portion is developed. These varia- 

 tions are more observable in Sert. pumila than in the Sea-thread 

 [Laomedea) . 



The formation of the ovarian vesicle, in this genus at least, 

 occurs in a very similar manner to what has been described in 

 the polype cell and trunk. The ovarian vesicles are cells formed 

 during the summer and autumn in situations varying with the 

 diiferent species ; and these having performed their function of 

 reproduction are periodically shed, to be replaced by others at 

 some future time. Their first appearance are small protube- 

 rances or elongations of the part on which they rest. At first a 

 darker appearance of the pulp and sheath is observed on the part 

 in which the vesicle is about to be produced. This is prolonged 

 precisely in the manner noticed in the formation of the polype 

 cell and trunk, and the separation of the pulp from the sheath 

 occurs also in the same manner. It increases in length to the 

 usual length of the vesicle, and with the exception that its axis is 

 larger, resembles a branch in everything. But instead of being 

 produced into a polype as in the polype cell, the surface becomes 

 marked with circular lines, which, as development goes on, as- 

 sumes the form of small grains or globules, more or less em- 

 bossed according to the stage of advancement. They rapidly 

 become more and more defined arid separated from each other, 

 but remain attached to the central pulp by an umbilical cord. 

 This also becomes more attenuated and finally gives way, and 

 the gemmule remains free in the horny case. These gemmules 

 have a central granular pulp surrounded by a semitranslucent 

 zone or case, and have their surfaces covered from a very early 

 stage of their formation with numerous vibratory cilia. In this 

 free state they remain in the case a short time, for the upper 

 portion of the vesicle opens and the remarkably active gemmules 

 revolve rapidly from spot to spot, as has been previously described. 

 From this it will be perceived that the function of these periodic 

 vesicles is reproduction, and therefore, when Prof. Forbes says 

 that their nature is unknown, he can mean only the ideal form, 

 from which he supposes them changed during their develop- 

 ment. 



