THE RELATIONSHIPS OF THE SEA-SPIDERS. 1 55 



Then the mandibles of the one group seem undoubtedly 

 homologous with the chelicerse of the other ; so also do 

 the palps of the one and the chelae of the other; there- 

 fore the trouble lies with the ovigerous legs. 



Schimkewitsch tried to solve the problem by sug- 

 gesting that this third pair came in as greatly developed 

 exopodite, or endopodite — I forget which — of either 

 the second or third pairs of appendages, and was there- 

 fore not equivalent to the other appendages. This was 

 ingenious, but wrong. The development of the ap- 

 pendages shows that the third pair is formed in line 

 with, and independently of, the other pairs ; and, more- 

 over, it has a separate pair of ganglia from its earliest 

 appearance. 



But there yet remains another possible explanation for 

 this third pair of appendages of the sea-spiders, viz. that 

 the spiders have lost a pair of appendages (and ganglia.?) 

 between the chelae and the first pair of walking-legs. 

 Here the objection arises that, although the develop- 

 ment of spiders has been quite fully studied, no evi- 

 dence of such a loss of appendages is forthcoming, and 

 therefore, for the present at any rate, we have to reject 

 this solution.^ 



The explanation which seems most plausible is, that 

 we cannot properly bring into line all the pairs of walk- 

 ing-legs and compare them, pair for pair, but that the 

 first pair of walking-legs of the spiders corresponds (as 

 in the table given above) with the ovigerous legs of the 

 sea-spiders, and, therefore, the second pair of legs of the 



1 Perhaps the development of spiders will bear re-examination in this 

 respect, and more especially should the first pair of ventral-ganglia be 

 examined to see if it is a single or a double pair. 



