THE PYCNOGONIDS. 31 



from the brain itself may be regarded as a more abbreviated 

 condition than what was seen (by Balfour) in the Spiders. 

 Metehnikoff's figures for Chelifer show the first pair of append- 

 ages to arise above and on each side of the proboscis-like upper 

 lip. If future work verifies Metchnikoff's suggestion that this 

 proboscis (riisselformige, provisorische Oberlippe) is homolo- 

 gous, entirely or in part, to the proboscis of the Pycnogonids, 

 as his figure might indicate, then does the whole development of 

 Chelifer show remarkably close resemblances to the Pycnogonids. 



6. The fourth pair of ambulatory legs — the seventh pair of 

 appendages — has been a stumbling block in the way of those 

 who have compared Pycnogonid with Arachnid. Semper and 

 Schimkewitsch have attemped to solve the difficulty by assum- 

 ing that the third pair of appendages of the Pycnogonids — the 

 ovigerous legs — are new structures, and then have called the 

 four pairs of walking legs homologous in the two groups. Prof. 

 Dohrn has shown the impossibility of dropping out in the count 

 the ovigerous legs, and has shown that this pair of appendages 

 are homonomous with the others. The two pairs of ventral organs 

 in the anterior larval ganglia we have seen point unmistakably 

 to the same conclusion and give the final proof, if such were 

 really necessary. 



We are led then to a comparison of the appendages of the two 

 groups, beginning with the chelicerse and going back pair for pair, 

 which leaves one pair over for the Pycnogonids. Any comparison 

 between the two groups must take into account this extra pair 

 of legs. Balfour has suggested that this last segment and its 

 appendages to represent the first abdominal segment of the 

 Arachnids. The third pair of appendages of the Pycnogonids 

 have assumed a special function, and at this time we might sup- 

 pose that an additional pair to have been added on from the 

 abdominal segments. We also know that the embryos of Spiders 

 have rudimentary appendages on the abdomen, and, as we have 

 assumed the Pycnogonids to have come from the latter group, 

 not recently but remotely, when these appendages may have 

 been larger or even functional, we have some ground for a belief 

 of such an origin of the last segment. 



There is another fact which may be of importance in this con- 

 nection. Not only is the seventh pair of ganglia carried dorsal- 



