Phyhgeny of the Arachnida. 299 



tubes are absent in the majority of the Amphipoda, and 

 since the Amphipods that possess them exhibit the already- 

 mentioned peculiarities in their mode of life *, we may suppose 

 that adaptation to life upon the shore or in water, which is 

 rich in oxygen, has occasioned the appearance of special out- 

 growths of the mid-gut, which, at least to a certain extent, 

 play the part of excretory organs ; such an adaptation might 

 appear independently in the representatives of the various 

 genera *, If we assume the same to have taken place in the 

 case of the ancestor of the Arachnids, in which the posterior 

 outgrowths from the mid-gut, which subsequently became 

 Malpighian tubes, first appeared, we must consider it to have 

 been a littoral form (such as Orcliestia). I have already 

 touched upon this latter question in considering the respiratory 

 organs of Arachnids f. 



The Malpighian tubes of the Arachnids consequently 

 develop from the posterior process of the mid-gut. This 

 process merits attention for its own sake, since neither the 

 Hexapods nor the Myriopods possess it. 



A comparison of the diiferent views as to the phylogenetic 

 relationship of the various groups of Arthropods has already 

 been furnished several times by a number of authors (Weissen- 

 born, No. 67 ; Fernald, No. 15 ; to some extent ZografF, 

 No. 71 ; Schimkewitsch, No. 58 ; and others). I shall 

 therefore notice only certain of the most important papers, 

 the authors of which are opposed to the separation of the 

 Arachnida from the Tracheata. If we glance at the litera- 

 ture of the last ten years we observe that since the appear- 

 ance of Ray Lankester's papers facts have continually been 

 collected from various sides in support of the relationship 

 between Limulus and the Arachnids. The most minute 

 study is devoted to the structure of the lungs of the Scorpion 

 and of the branchiaj of Limulus, to the development of these 

 organs, the modification of the appendages in the Aranese, 

 the structure of the blood-vascular and. nervous systems, the 



originally lived at the mouths of small rapidly running streams, which 

 flow into the sea, at the point where the river-water, meeting the waves, 

 forms a perpetual surf. 



* In Melita we find only a single unpaired process of the mid-gut, in 

 the other forms two ; yet, as is well known, ditFerences of this kind also 

 occur between the Malpighian tubes of the Acarina. 



t In the handbook of Steinmann and DiJderlein (No. 62) the following 

 passage occurs (p. 512) : — -"The majority of the palaeozoic Arthrogasters 

 were aquatic forms ; the oldest among them, at any rate, were marine ; 

 while the later forms, in part those existing at the present day, are 

 without exception adapted to sojourning in the air" (w'cZe also p. .^OO). 

 Why the authors represent this view it is impossible to explain. 



