MORPHOLOOIOAL METHOD AND RECP:NT PRoaRKSS IN ZOOLOGY. (iOf) 



hhiiic ot" r<>niis. Ill }):issiiij^- rroiii (lie lower to the liiiilicr C'rustticea, 

 we find this fusion increiisiiiu- as we Hsceiid; and it theret'oro, 

 l)ocoines necessarv to compare the Scorpion with tli(> other Arachnida, 

 Limidus with tht^ Kurvptorifbi, in older the liettcn- to doterniine the 

 position of eacli in its respective series ])y the a[)[)lication of this 

 rule. 



As to the nunil)er of seeinents present, variation is a matter of small 

 concern, in consideration of the mode of orig'in of segmentation and 

 the Avide numerical range — from seven in the Ostracods to more than 

 sixty in Apus - the st^gments of the crustacean class present. 



On the arachnidan side, in the Solifugte l)iit the third and fourth 

 segments are fused; the remaining four of the prosomal series with 

 the ten which remain are free. Tn Kn'iKiua four of the prosomal seg- 

 ments alone unite; the fifth and sixth Avith the rest are free. And 

 when we pass to the Limuloids and the descending series of their 

 allies, we find it distincti^'e of the Eurypterida that all the opistho- 

 somal segments are free. If we can trust thes<> comparisons, w^e must 

 conclude that the Eurypterida of the past, in respect to their segmen- 

 tation, simplify the Limuloid type, on lines similar to that on which 

 the 8olifugi\3 and Kcenenia simplify the Higher Arachnid and Scor- 

 pionid type, and that therefore if the degree of antero-posterior fusion 

 of segments has the significance attached to it, L'ntmlnx and Scorpio 

 must each stand at the summit of its respective series. If this be 

 admitted, it has next to be asked if, in comparing them, we may not 

 be comparing culminating types, which might Avell be isomorphic. 



The scorpions are known fossil by two genera, PaJceopJionus and 

 Prof<cor2^tt/s^ from the Silurian of Gotland and Lanarkshire, the Pent- 

 land Hills, and New York State; while recenf research, in the discov- 

 ery of the genus Sfralwps, has traced the Eurypterida back to the 

 Cambrian, leaving the scorpions far behind. One striking feature of 

 the limbs of the Pala?ozoic Eurypterids is their constantly recurring- 

 shortness and uniformly segmented character, long known in Sliino- 

 nla^ and less conspicuously in Pferygotii.s itself, retained with devel- 

 opment of spines in three of tive known appendages of the recently 

 described eurypterid giant Styfonurns. The minimum length yet 

 observed for these appendages is that of the Silurian species Euvup- 

 terus fischerl^ discovered by Holm in Russia in 1S!)S. This creature 

 is one of the few eurypterids in which all the api)endages are pre- 

 served, and it is the more strange, therefore, that tiie advocates of the 

 arachnid theory should ignore it in their most recent account. Allow- 

 ing for the specialization of its sixth prosomal appendage for swim- 

 ming, the tifth is but little elongated; the second, third, and fourth 

 are each in total length less, by far, than the transverse diameter of 

 the prosoma, and unifonnly segmented, giving the appearance of 



