186 



KNOWLEDGE 



[Adodst, 1902. 



oxclusively marine. An exception mif,'ht be suspected in 

 PiiUeiiopsin IhimineiiKis (Kriiyer), which owes it.s specific 

 tiaine to the word Kio, a river, liut Kn'iyer, who gave the 

 name, explicitly states that the species was taken in the 

 sea, iu the nautical roadstead of Rio Jaueiro. Future 

 researches may find isolated members of the group living 

 in fresh water or on dry land, but in the meantime the 

 waters of the ocean, with their depths and shaDows, 

 straits and inlets, and the s])ace between tide-marks along 

 the curves and indentures of an almost immeasurable 

 coast-line, offer a hunting-ground not likely to be soon 

 exhausted. In ])articular localities of this vast field some 

 spirics are said to be common or very abundant. Some 

 s|ii(ics are widely distributed. Speaking of them as a group 

 Dr. Dohrn says that "they belong to the most frequent 

 auimal forms included iu the shore-fauna of all seas : you 

 can scarcely examine a handful of sea-weeds, a few 

 fragments of submarine gravel, or materials from the 

 hauling of a dredge, without lighting upon one or more 

 species of these little creatures." Still, as a rule, they 

 seem to be a feeble and saittered folk, and yet, though 

 their numbers are relatively few, they easily fall into the 

 hands of the collector. An explanation of this may be 

 suggested. In spite of their long legs they have no speed 

 of motion, nor do they, like many children of the sea, 

 practise varied tricks of evasiveness. Interference will 

 induce them to crumple up their many-jointed limbs, but 

 will not provoke them to show fight, for which they are 

 jworly endowed. One may infer from all this that their 

 enemies are not numerous or pertinacious. Man has been 

 neglectful. Other devourers may have found by expe- 

 rience that there was no satisfactory nutriment in their 

 long branching tubes of chitinous, or as Eights calls it 

 " pergamineous " integument. They won't fatten. Never- 

 theless, like other animals, they have obeyed some 

 stimulus impelling them to vary. Assuming that all are 

 traceable to a common ancestor, we may ask which of the 

 existing species are nearest to the original form, or which 

 are the most remote from it. As so often happens in 

 genealogies, there is a deplorable want of trustworthy 

 documents. Fossils at present give no assistance. The 

 larval stages cannot be expected to speak with other than 

 a lisping voice. Existing species must be compared and 

 cross-examined, and even then the antiquity of common 

 characters is rendered uncertain by the chance that some 

 may have heen independently developed more than once. 

 or have come again into evidence after a period of 

 disappearance. 



If we are searching not for the most but for the least 

 characteristic genus, some avithors not unreasonably 

 direct our attention to Pycnogonum. It was a singular 

 fate which brought this first into scientific notice, gave to 

 this first a technically valid name and thus made it the 

 premier genus of the grou]>. For instead of being a 

 good representative, it appears to have gathered about it 

 as many exceptional attributes as it could. Most of the 

 Pycuogonida have very slender bodies and very long legs. 

 Pycnnr/oiiHiii. delights to have the body stout and the legs 

 rather stumpy. All the other genera find sjsace within 

 the body for a heart. Pycnogonum, in which the body is 

 more than usually roomy, goes without one. Commonly 

 the eggs when laid are divided between the two ovigerous 

 legs of the male ; in Pycnugonum both these legs are used 

 for carrying a single egg- clump. The normal complement 

 of limbs in the Pycuogonida, as we have seen, is seven pairs; 

 I'ycnogomtm belongs to the anomalous section which 

 exhibits only five pairs in the male and no more than four 

 in the female. It has been heretofore explained how this 

 genus flies in the face of custom by having no genital 

 openings in the second joint of any but the last pair of 



legs, and there it has them sometimes contrary to usage in 

 the upper instead of the lower surface of the joint. It 

 goes further, and conspires with one other genus, Dohm's 

 Bnrana, to flout the speciality of its tribe h>y developing 

 ova not only along the legs but also in the body. 



^^^ 



Pycnogonum httorale (Strom)?. From Sars. 



It might be argued that the characters displayed in 

 Pycnogonum are primitive, and that the contrasted genera 

 have in these respects departed from the earlier type. It 

 is almost certain, for instance, that, before the expedient 

 of developing ova in the legs came into play, the normal 

 method of developing them in the body will have been 

 followed by many an ancestress of the tribe. On the 

 other hand that normal method may have fallen into 

 disuse and after a long interval been revived. That the 

 genital ojjenings were originally a single pair is at least 

 conceivable, but again it would not follow that the single- 

 ness in Pycnogonum must be regarded as original. To 

 believe that females without the first three pairs of 

 appendages are of an earlier type than those which have 

 them would require a very robust faith. It would imply that 

 the ovigerous function of the third pair in the males was 

 primitive, whereas it is much more likely that this function 

 was transferred from the females, and that the egg- 

 bearing sex suffered loss of the egg-carrying Umbs owing 

 to disuse. Still more decisively is the view that 

 Pycnogonum has had losses rather than that the other 

 genera have had gains, supported by the facts connected 

 with the first pair of appendages. These are wanting in 

 adults of both sexes not only of Pycnogonum but of 

 various other genera, and in many are found to be small 

 and rudimentary. But, as explained in the preceding 

 chapter, the larval forms all have these appendages, and, 

 more than that, they all have them chelate. It would be 

 difficult, therefore, to resist the inference that this pair 

 at least is an original part of the organism. The cir- 

 cumstance that in some instances it dwindles and loses its 

 chelate character in the adult, without disappearing 

 altogether, gave rise to a very natural mistake. A genus 

 Ammothea was founded by Leach on the young, and 

 subsequently a genus Achelia by Hodge on the full-grown 

 specimens of congeneric s|iecies, and these two genera, 

 which are really one and the same genus, were even 

 recently and by an approved author placed iu separate 

 families. It is no reproach to the systematist that he 

 should fall into such errors while feeling his way towards 

 a natural classification. The hand of man is a structure 

 to which the human race is so incalculably indebted for 



