330 Mr. C. Spence Bate on the Development of the Cirripedia. 



induces the idea that it adds a pair of legs with each successive 

 moult ; but this link in the history of the young creature's de- 

 velopment is yet to be made clear. 



At the anterior base of these organs an opake spot exists 

 (fig. 15 a), which I presume to be the stomach. 



Two larger and darker spots, situated a little higher and an- 

 terior, are pronounced to be organs of vision ; near these are 

 inserted two long slender members which are supplied with 

 a sucker and hooks to each limb ; with these the animal has 

 the power of attaching itself to any object, and, by using them 

 alternately, of perambulating on the surface of any hard sub- 

 stance ; thus the young creature is in the middle stage endowed 

 with the power of walking as well as swimming. 



Here I cannot help remarking upon the gradually changing 

 habits of the creature, which in its early state swims about at 

 its own will and pleasure, using, as all aquatic creatures do, its 

 long tail as a rudder, by which it is enabled to direct and con- 

 trol its own movements ; whereas in the latter stage of its larval 

 existence the tail is gone, and consequently the creature is most 

 excentric in its movements through the water, apparently being 

 unable to swim direct to any fixed point. Thus it appears that 

 before it becomes a sedentary animal it has been partially ren- 

 dered incapable of fully enjoying its existence as a swimming 

 creature, and thus the path is softened in the change of habits 

 from an active to a stationary existence ; for an animal not having 

 power to control its movements in its natural element could 

 scarcely be supposed to enjoy its own existence : thus, under these 

 circumstances, to become stationary is to become more happy. 



It is I believe generally understood that at this stage the larva 

 has two valves, one on either side, a right and left, united at their 

 posterior margin by a hinge similar to that of a bivalve among 

 Mollusks. 



Of the correctness of this I was far from being able to con- 

 vince myself, insomuch that I could neither observe the hinge 

 nor the separation of the valves beyond a certain point at which 

 the two appeared to me to unite ; nor could I observe any open- 

 ing or shutting, the two sides appearing to me to be continually 

 the same, and the whole together formed a shelly cell such as I 

 have endeavoured to figure (PL VIII. fig. 17). 



At this period the larva may be presumed to represent the 

 adult animal, and the shells of the operculum, but without the 

 accessory valves. 



Thus it is to be remarked, that this animal in its growth from 

 embryo to adult puts on several distinct characters, all of which 

 are indicative of the Crustacea in different forms. 



