48 HALF-AN-HOUR AT THE MICROSCOPE. 



mostly lives on. Just for the same reason as the mountain- 

 climber on ice gets a pair of boots with strong, sharp spikes in 

 their soles to enable him to retain a firm footing on the treacher- 

 ous surface he moves on. 



Animal of Barnacle (PI. VII., Fig. 6). — By the kindness of 

 Charles Darwin, I have been enabled to consult original speci- 

 mens and figures prepared for his (Ray Society) work on the 

 Cirripedia. The history of the creature reads like a romance. 

 When first hatched, it is a free swimmer, in shape like a kite with 

 six legs, the two hinder pairs forked (Fig. 7., PI. VII.). After 

 successive moults, it settles on its head, the antennae lay hold of 

 what the creature considers a suitable object for adherence to, 

 cement-glands at their base pour out a secretion, and thenceforth 

 what is known as " retrograde metamorphosis " takes place. The 

 head becomes, so to say, lost, as well as the abdomen ; the part 

 that is left is thoracic ; the shell, the thoracic shield. Of the five 

 pairs of limbs left, the first appears to assume the functions of the 

 lost antennae. " Each of the cirrhi is composed of a series of 

 semi-corneous pieces, exhibiting at each joint long, stiff hairs. 

 Every pair of cirrhi arises from a single prominent stem, and 

 those most distant from the mouth being the longest and most 

 ostensible, the whole apparatus, consisting of twenty-four " (twenty 

 here, I think ; another species is under description), forms, when 

 protruded from the body, a kind of net of exquisite contrivance, 

 in which passing particles of nourishment are easily entangled, and 

 thus conveyed to the mouth. The latter is seated on a prominent 

 tubercle, and is composed of three pairs of mandibles, the two 

 outer horny and serrated, and of a lip with rudimentary palpi. 

 The digested food passes out through an orifice behind and at the 

 base of the last pair of cirrhi. Arising from this part is seen a 

 long, flexible organ, the nature of which has much puzzled inves- 

 tigators ; it has been taken for a tail^ a petiis^ an ovipositor. The 

 latter supposition appears to have most to support it. There are 

 good grounds for believing that an eye is present. " Mr. Darwin 

 observes, vision seems to be confined to the perception of the 

 shadow of an object passing between them and the light ; they 

 instantly perceive a hand passed quickly at a distance of several 

 feet, between' a candle and the vessel in which they may be 

 placed." There is also an organ of hearing of a simple kind. 

 Our limits will not permit of more extended remarks here. A 

 good summary will be found in Rymer Jones' " Outlines of the 

 Animal Kingdom," pp. 449 — 463, ed. 1861. 



TuFFEN West. 



