169 



Note on the Function of the Spines of the Crustacean 



Zooea. 



By 



W. F. R. Weldou, M.A., 



Fellow of St. Joliu'ij College, Cambridge; Lecturer on luvertebrate Morphology in 



the University. 



With Plate XVI. 



Anyone who has examined the so-called '' protective " spines of 

 the various Zoaea larvje must have been struck by their great ten- 

 dency to develop in one straight line, parallel to the long axis of the 

 body. Among the Macriira this is the case in the Zooea of Feneus, 

 in the larva attributed by Claus to Hiii^olyte, and in the Galatheidge. 

 In the Brachyura the same result is attained in a slightly different 

 way. 



A comparison between the behaviour of those forms which are 

 provided with long spines and those which are devoid of them, will 

 show clearly that these structures have at least one function which 

 has not, I believe, been hitherto recognised. 



The accompanying drawing was taken from a Portunid larva, seen 

 obliquely from above while in the act of swimming. The larva is 

 seen to lie upon its back, and to swim in the direction of the arrow 

 by rowing itself along with its maxillipeds, exactly in the manner of 

 two' men sculling a narrow racing boat. Steering is effected by 

 means of the tail. 



The great majority of the Brachyurous larvae which I have ob- 

 served swim in this manner, though some of them do not lie upon 

 their backs. 



If a number of Decapod larvae be placed together in a large glass 

 vessel, the effect of these spines upon their swimming capacities is 

 very manifest. Such a larva as the Portunid of the figure will swim 

 in an absolutely straight line towards the light, moving with great 

 rapidity, and neither changing his direction nor losing his equilibrium 

 during a journey of several feet. Those larvae without spines, on 

 the other hand, such as Crangon or Palunmon, will make their journey 

 .tjieir jo«F»ey towards the light in a very different manner. Their 



