4 o SCIENCE PROGRESS. 



lengthening alike, the antennae as well as the legs. The 

 specimens of Triarthrus, then, were found with a pair of 

 cirriform antennae projecting- from under the head shield, 

 and a confused fringe of appendages protruding, along each 

 side to the posterior end of the body, from under the dorsal 

 shield. The fact that the antennae came from under the 

 head shield was important, as the antennae of Apns are 

 attached under the head shield on each side of the pro- 

 stomium or large upper lip, whereas, as a rule, among the 

 higher Crustacea, the antennae are placed quite anteriorly. 

 And, as a matter of fact, examination of fortunate specimens 

 showed that the antennae were inserted in Triarthrus in 

 practically the same relative position to the prostomium 

 as they are in Apus. 



If verifications of predictions based upon a theory are 

 proof of the correctness of that theory, here was the proof 

 of the relationship between Apus and the Trilobites. That 

 relationship had been based upon other resemblances of 

 organisation, some of the more important of which have 

 been briefly indicated above, and little more than a year after 

 the antennae of the Trilobites were found exactly where it 

 was predicted they would be found. The importance of 

 this point will be understood when it is remembered that 

 no other known Crustaceans, recent or fossil, except Aptis 

 and the Trilobites, possess the great square labrum point- 

 ing backwards, with the antennae inserted on each side of 

 it, the whole hidden under a great head shield. 



Before passing on to the next point, this ventral position 

 of the antennae and labrum deserves attention. Occurring 

 in Apus with its traces of sixty segments, and in the Trilo- 

 bites, the oldest fossil Crustaceans, no one can doubt that it 

 is the primitive position of these organs in the crustacean 

 phylum. It follows, therefore, that the annelidan ancestors 

 of the Crustacea, with their originally anteriorly placed 

 prostomium, must have bent the first segment sharply 

 round in order to bring that organ into the ventral posi- 

 tion found in the primitive Crustacea. There is, in fact, 

 abundance of evidence to show that such a bending did 

 take place. Without going into details which have been 



