506 E. W. MAOBRIDE. 



impossible to see exactly what happens to the anteiinules, but 

 by carefully examining the shorter darts, which are carried out 

 at a more moderate speed, it is seen that the antennules are 

 held as rigidly as during the slow movement, and there is 

 therefore no ground for attributing any share in the produc- 

 tion of the movements of these animals to the first antennae. 

 Naturally when the animal is suddenly propelled forward the 

 tips of these appendages will be mechanically dragged back by 

 the resistance of the water ; and a careless observation of this 

 phenomenon, joined to the undoubted fact that in the fresh- 

 water Cyclops the first antennae do assist in the slow move- 

 ments of the animal, may have given rise to the belief that it 

 was the rule among Copepoda to propel themselves by means 

 of the first antenna. 



In a paper published some years ago (Sedgwick's theory of 

 the embryonic phase of ontogeny as an aid to phylogenetic 

 theory, ' Quart. Journ. Micr. Sci.,' 1895) I put forward the view 

 that the progressive development of the Crustacea was corre- 

 lated with a passing of the function of locomotion backwards 

 along the series of appendages. Thus, in the ancestor repre- 

 sented by the Nauplius, the first, and more especially the second 

 antennae were the main locomotor organs ; in the stage^repre- 

 sented by the Zooea the maxillipeds had acquired the function ; 

 whilst in the ancestral condition corresponding to the Mysis 

 larva, motion was effected chiefly by the hinder thoracic legs, 

 as is still the case with Schizopoda; finally, the lower Macrura 

 swim by means of the abdominal appendages alone. The result 

 of this process has been that the appendages of the anterior 

 segments have been one by one relieved of the function of loco- 

 motion, and have become specialised for masticatory and sensory 

 purposes. Now in the Nauplius the main brunt of the work of 

 locomotion is borne by the second antenna ; the first is already 

 mainly a sensory organ, and if the Copepoda really did propel 

 themselves chiefly by the first antennae they would have retro- 

 graded from the condition represented by the Nauplius. It is 

 interesting to note that not only is this not the case, but that the 

 second antenna is still an important locomotor organ. Func- 



