NATURAL HISTORY OF AMERICAN LOBSTER. 



333 



and often successful capture of copepods and other members of the plankton or floating 

 population, showing that they can direct their movements with a certain degree of 

 precision when necessary or when the light and other conditions are favorable. 



The body of the little lobster is armed at most vulnerable points with defensive 

 spines, and its various appendages bristle with tactile hairs or setae, as well as with 

 more diminutive spines, which may afford some slight degree of protection against 

 smaller enemies when they do not assist 

 it in seizing and tearing its prey. 



The free margin of the "paddle," 

 or forked telson plate, as commonly 

 seen in the larvae of the higher Crus- 

 tacea, is garnished with very uniform 

 and symmetrical spines and plumose 

 hairs. 



It is interesting to observe that cer- 

 tain spines and the setae whatever their 

 size or function, from the rostrum or 

 tips of the claws down to the smallest 

 microscopic hair, agree in their essen- 

 tial structure, and are all developed as 

 tubular folds or outgrowths of the 

 integument. In the course of the pre- 

 natal molt all the spines as well as the 

 hairs are telescoped or invaginated. 

 (Compare p. 269-270.) 



In swimming the young lobsters 

 use the outer branches or exopodites 

 of the thoracic Umbs (segments ix-xrv, 

 table 4) , by the beating movements of 

 which they are slowly driven upward, 

 downward, orforward (compare fig. 40), 

 and the abdomen, by the sudden fold- 

 ing of which and by the aid of its broad 

 telson plate, they dart rapidly back- 

 ward. Each thoracic leg, in conformity 

 to the type of decapod limbs, consists 

 of a short stalk or protopodite and two diverging branches, the outer branch or exopodite 

 which serves as a flexible "oar," being flattened and fringed with long feather-like hairs. 



The "oars" work independently of the inner branches, which in the larva are 

 mainly prehensile organs, and which with the stalk alone give rise to the adult limbs. 

 The concerted vibratory strokes of these minute flexible oars is so rapid and so uniform 

 in vigorous larvae that at a short distance from the eye it is impossible to follow their 

 movements. 



I^IG. 37, 3S, and 39. — Parts of seUe from cheliped of larval lobster, 

 showing different degrees of reduction from typical plumose 

 type. Enlarged Ss times. 



