162 Mr. 11. Q. Couch on the Morpliologij of Zoopliytes. 



which the poh'pes or prehensile portions are situated. The 

 polypes are attached inferiorly to the central granular pulp which 

 ramilies through the centre of the trunk and branches^ and are 

 indeed formed of it. These are the only portions of the creatures 

 exposed to the influence of the surrounding water^ and by these 

 the food is taken, digested, and the nourishment distributed to 

 all the other parts. In many species the polypes are exceedingly 

 numerous, but though they are entirely independent of each other 

 as regards their individual life and nourishment, yet they can- 

 not be considered as distinct animals ; for the whole production 

 seems to be but one compound creature, derived from the same 

 source, the pulp and all tending to carry out the same object. In 

 this respect they resemble trees ; each branch is independent of 

 all the others and may be cut off without injmy to the whole, 

 and yet all together they constitute the perfect polj'pidom. At 

 particular seasons, extending from the middle of summer to 

 autumn, and in fine weather to the early parts of winter, there 

 are other and differently shaped cells developed, which are larger 

 than those previously mentioned as containing the polypes. These 

 are the ovigerous vesicles, which after having performed their 

 function drop off and disappear. In this they differ from most 

 other animals, in which the reproductive organs are, in duration, 

 coextcnded with the lives of the creatures, and offer a remark- 

 able analogy to similar parts in plants both in their decay and 

 periodical re-appearance. " These organs," Professor Forbes says, 

 " in theu' nature, have often been discussed but never explained.^^ 

 By their natm'e the Professor cannot mean the function they 

 perform in the oeconomy of the creature^s existence, since that is 

 established by numerous and accurate observations ; but rather I 

 presume the nature of the tyjie from which they have undergone 

 their ideal metamorphosis. In this he is certainly correct, and 

 the present observations are intended to elucidate this, and in 

 some measure to extend it. The reproductive gemmules are very 

 minute globular bodies, surrounded by numerous \-ibratory cilia 

 which are in constant action. The mode in which they are 

 formed will be briefly described hereafter. As soon as they have 

 escaped from the ovigerous capsule into the surrounding water, 

 they move about \\\t\\ great rapichty in a revohing manner, like 

 the earth on its axis. While examining them in a bottle I could 

 perceive that they occasionally stopped, and then again would 

 rapidly move from spot to spot. In this way they move about 

 from one horn* to nearly two days, depending apparently on the 

 temperature and the nature of the surrounding surfaces. They 

 would occasionally rest on the glass for a few minutes, and then, 

 as if the spot was an unfavourable one, again start off and revolve 

 as rapidly as before, frequently changing their form from the cir- 

 cular to the oval ; sometimes acquiring an hour-glass contraction, 



