140 



KNOWLEDGE. 



[June, 1902. 



pair of appeiulatfi's remains inystorions. The miiiutiaj of 

 their structure, witliout makint; much a])pi'ai to the unaided 

 eve, show some striking and beautiful eharai-ters under the 

 microscope. Tiie weak-looking joints at the end of the 

 limb are usually bordered with rows of spines, of which 

 the varied sculpture would scarcely be suspected until it has 

 been seen under a high magnification. The numbers and 

 shapes of these leaf-like and sometimes strongly denticu- 

 late spines are helpful in generic distinction. The number 

 of them may be (juite trivial or it may amount as in 

 Cnlogsemlein (jirjae, Hoek, to several hundn>ds. The worn 

 condition of the apparatus in the specimen figured implies 

 a period of active service, and considering that the species 

 in question is capable of growing legs twelve inches long, 

 it mfiy well be that the cleansing appendages find them- 

 selves severely taxed in brusliing up and keeping trim all 

 the four jiairs. 



Unlike the organs already discussed, the ambulatory 

 limbs, with only one known exception, have always the 

 same number of joints, which is nine. Gnamptorhynchus 

 ramipes, Biilim, is without the terminal joint in the first 

 pair. Of the nine joints, the middle three are almost 

 invariably the longest. In other respects there is abun- 

 dance of variation, distinguishing legs that are stumpy 

 from legs that are of a marvellous attenuation, legs that 

 are spiny from legs that are smooth, and especially legs 

 that have the ninth joint or claw accompanied by a couple 

 of auxiliary claws from legs that have no such accessories. 

 Dr. Meiuert says, "These auxiliary claws are really the 

 terminal claws of the foot, originating from and attached to 

 the last joint (the claw) of the foot. In so far they are real 



Spines 



iiiiitli jiiiiif. oi' oviycroutt 

 JIi{;lily niiignified. 



log; Colossciuleis yiyas, Hocli 

 irom Hoek. 



claws, and correspond to the claws in the Arachnida and most 

 Insects. Corresjionding claws are wanting in the Crustacea, 

 and therefore their presence in the Pycnogonida is of no 

 small systematic importance; it is to be remarked, however, 

 that they often become rudimentary or quite disappear, 

 but, nevertheless, they may be said to be typical in this 

 group of animals." As qualifying this view it should be 

 borne in mind that supplementary claws are not unknown 

 among Crustacea, at least as occurring on the inner side of 



the principal unguis, while on its outer side the Ainphipoda 

 quite usually have a seta at the very ])oint at which in 

 pycnogonids the auxiliary spines originate. But between 

 setae and spines nature has left no interval unbridged. 



To complete the account of the ap])endage8, the patient 

 reader must allow his thoughts to be transferred to the 

 time when the young pycnogonid is just escaping from the 

 egg and still trusting to the benevolent support of its 

 father's arms. Between the emerging larva, more compact 

 than graceful, and the parent, usually with long, slim, 

 radiating limbs, there is almost no resemblance. In the 

 earliest stage, which may exceptionally be passed within 

 the egg-cover, the little creature has no abdomen, but a 

 swollen trunk and three pairs of ajjpendages, this latter 

 characteristic suggesting a comparison with the crustacean 

 nauplius. But here the first pair are chelate, and the 



li ( 



L;irva of Pi/cnoponum lUtorale, Brunnieli. ^Vftor Krbjer. 



two following pairs are simple, not two-bi-anched as in the 

 nauplius, so that the difference is very substantial. With 

 the progress of development the four pairs of walking-legs 

 successively ajripear. But in the meantime, according to 

 Meinert, the second and tbii-d larval appendages are 

 thrown off, and then the " palps" and " ovigerous legs " 

 come on to the scene, Meinert's theory being that these 

 are not representatives of the two discarded larval pairs, 

 but of quite independent origin. Hence he affirms that 

 the typical number of j>airs of limbs in the Pycnogonida 

 is not seven but nine, Of these nine, he holds that the 

 last four pairs " are not at all homologous with the 

 ambulatory legs of the Arachnida, but in all likelihood 

 with the four pairs of small processes that have been 

 pointed out in the abdomen of the Arachnid-embryo." 

 Taken altogether, the arguments he uses to justifv his 

 classing this group among the Arachnida may rather 

 incline observers to leave him in this respect ploughing a 

 lonely furrow. In 1891, Prof. G. 0. Sars expressed the 

 belief " that all naturalists are at present unanimous that 

 those animals [the Pycnogonida] can neither be referred 

 to the Crustaceans nor the Arachnidans, but must form a 

 class by themselves." 



Future researches may at any time remove the group 

 from its splendid isolation. For the present, in regard to 

 external relationships, we shall do well to leave it alone in 

 its glory. Within its own confines there remains to be 

 considered the relative importance of agreements and 

 differences on which the distinctions of its species, genera, 

 and families have been founded. 



