630 PROFESSOR E, RAY LANKESTER,. 
tive of the special adaptations of those organs to an aquatic 
or aérial mode of life. 
The second agreement, viz. that as to the existence of 
compound eyes, is more apparent than real; for it is quite 
obvious that a coming together of simple eyes might at any 
stage in the evolution of Arthropods produce a compound 
eye, whilst further in the actual details of structure of its 
compound eye, Limulus is altogether unlike the Crustacea. 
The resemblance of the compound eyes in the two cases is a 
superficial one, due to homoplasy.! 
The third agreement is of a purely negative character. 
Limulus and the Crustacea may have independently lost the 
Malpighian tubules which were perhaps possessed by the 
earliest ancestral Arthropods ; or, on the other hand, these 
organs may have developed for the first time in the terrestrial 
Arachnida, and have been derived from them by the other 
Arthropoda which possess them (Hexapoda, Myriapoda) ; or, 
again, the latter may have also developed such organs de 
novo. In any case their absence from Limulus is no evidence 
of affinity to Crustacea. It is to be noted that the smaller 
terrestrial Arachnida are also devoid of these organs. 
It will now be convenient briefly to point out and criticise 
some of the views which have recently been expressed as to 
the affinities of Limulus. 
Dohrn (1), in 1871, whilst pointing out at some length 
the affinities of Limulus and the Eurypterina, originally 
suggested by MacCoy and placed on a firm basis by Hall, 
and also whilst demonstrating some of the relationships of 
the larve of Limulus to Trilobites, proposes to unite these 
forms in one group—-Gigantostraka (a name originally pro- 
posed by Haeckel for the Eurypterina alone), and to place 
this group near the Crustacea, not absolutely within that 
class. | 
Although Dohrn cites the views of Straus Durkheim, he 
does not support them, and definitely states that we are not 
in a position to say what may be the relationships of Gigan- 
tostraka to Arachnida. 
Dohrn holds that the first pair of appendages of Limulus, 
though not the second, is innervated from the cerebral gan- 
glion, but he is free from the erroneous conception of the post- 
anal spine of Limulus as representing a series of segments. 
At the same time he failed to be struck with the exact 
identity in the number and disposition of the segments 
which is revealed when Limulus and the Eurypterina taken 
1 See ‘Annals and Mag. of Nat. Hist.,’ July, 1870, on the use of the term 
“ Homology.” 
