392 



Prof. E. R. Lankester. 



[June 16, 



tures in Limulus, which appear to me to be strongly confirmatory of 

 the identification of the structural elements of that animal with the 

 structural elements of Scorpio; and, pending the preparation of a 

 more complete account of the matter, I am anxious to place on record 

 the chief grounds which appear to me to exist for classifying Limulus 

 with the Arachnida in very close association with the pulmonate 

 members of that class. 



Without depreciation of the morphological insight of those who 

 have previously approached this question, amongst the foremost of 

 whom are the English zoologists, Huxley, Woodward, and Owen, I 

 may venture to say that it appears to me that the fact that Limulus is 

 little else than an aquatic scorpion, and Scorpio little else than a ter- 

 restrial king crab, has not as yet become an accepted conclusion of 

 zoological science, because those zoologists who have discussed the 

 question and instituted a comparison between Limulus and Scorpio — 

 whether (as Straus Durckheim) favourable to their association or (as 

 every other zoologist) opposed to it — have not to begin with hit upon 

 the true terms of comparison. We have in Limulus, on the one 

 hand, and in Scorpio, on the other, a series of more or less completely 

 expressed body-segments and a corresponding series of appendages. 

 Everything depends on making a correct start in the comparison, sup- 

 posing that a very close agreement exists between the two series in 

 a barely masked condition, and is to be made evident as the result of 

 the comparison. 



The notions as to the importance of the innervation of appendages 

 from a ganglion lying in front of the mouth as opposed to the condi- 

 tion when innervation proceeds from a ganglion behind the mouth, 

 have tended to obscure the true relationships of Limulus and Scorpio. 

 For it is only quite recently that it has been established (Alphonse 

 Milne-Edwards) that the ganglion in front of the mouth does not 

 innervate the first pair of appendages of Limulus* and that, similarly, 

 the innervation of the first pair of appendages (cheliceree) of Arach- 

 nida does not proceed from the primitive " ganglion in front of the 

 mouth "; but from right and left lateral nerve-centres, which are 

 embryologically quite distinct from the primitive praeoral ganglion, 

 and posterior to it (Balfour). 



Whilst there has been a difficulty in regard to this point of com- 

 parison, which is now removed, there has not been a full and well- 

 grounded conviction of the identity in structure and position of the 



* [June 24th, ]881. I am able fully to confirm the exactness of the account of 

 the nervous system of Limulus given by M. Alphonse Milne-Edwards, having, 

 through the kindness of Mr. Carrington, F.L.S., received from the Eoyal West- 

 minster Aquarium a living specimen of Limulus, which enabled me to dissect out 

 the relations of the nerves to the ganglionic centres in the most satisfactory 

 manner.] 



