The evolution theory . e blood of their hosts (Fig. 112, C. ISacc). Theypossess neither head, nor thorax, nor abdomen, not even an indicationof segmentation, no limbs of any kind, neither antennee, nor mouthparts, nor swimming-legs. Nevertheless they are Crustaceans ; indeed,we can say with certainty that they belong to the order of Cirrhi-pedes, for they leave the egg in the form of a nauplius larva {A),with horns on their carapace which no other forms except them-selves and the Cirrhipedes possess. That they are of the same stockas these is also proved by their further development, for the n
The evolution theory . e blood of their hosts (Fig. 112, C. ISacc). Theypossess neither head, nor thorax, nor abdomen, not even an indicationof segmentation, no limbs of any kind, neither antennee, nor mouthparts, nor swimming-legs. Nevertheless they are Crustaceans ; indeed,we can say with certainty that they belong to the order of Cirrhi-pedes, for they leave the egg in the form of a nauplius larva {A),with horns on their carapace which no other forms except them-selves and the Cirrhipedes possess. That they are of the same stockas these is also proved by their further development, for the naupliusgrows first, just as in the case of the Cirrhipedes proper, into a Cypris-like larva {B), so called because it bears a certain resemblance to theOstracods of the genus Cypris, and only from this point do their pathsof development diverge. The Cypris-like larva of the true Cirrhipedessettles down somewhere, attached by its antennge; it grows, and itsbody becomes that of the perfect Cirrhipede; but the Cypris-like. 168 THE EVOLUTION THEORY larva of* the Sacculinae bores its way into the inside of a crab orhermit-crab, at the same time losing its limbs, segmentation, and itschitinous covering; and within the body of its host it is transformedinto the sac-like organism we have already described. After a time itemerges again on the surface, and remains attached to the abdomen ofits host (Fig. 112, C. Sacc), drawing its nourishment from the bloodwhich it sucks up by means of its numerous delicate roots (W, W). From all this we may conclude that certain Cirrhipedes in timeslong past adopted a parasitic habit in the Cypris-larva stage, and thatthey gradually underwent adaptations to this mode of life, and thatthese went further and further, until the animal was transformed
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Keywords: ., bookauthorthomsonj, bookcentury1900, bookdecade1900, bookyear1904
