14 HISTOEY OF CRUSTACEA. Chap. III. 



this discovery gave me ttie first decided turn in Dar- 

 win's favour. 



The similar number of segments ^ occurring in the 



1 Like Claus I do not regard tlie eyes of the Crustacea as limbs, and 

 therefore admit no ocular segment ; on the other hand I count in the 

 median piece of the tail, to which the character of a segment is often 

 denied. In opposition to its interpretation as a segment of the body, 

 only the want of limbs can be cited ; in its favour we have the relation 

 of the intestine, which usually opens in this piece, and sometimes even 

 traverses its whole length, as in Microdeutopus and some other Amphi- 

 poda. In Microdeutopus, as Spence Bate has already pointed out, one 

 is even led to regard small processes of this tubular caudal piece as 

 rudimentary members. Bell also (' Brit. Stalk-eyed Crust.' p. xx.), 

 states that he observed limbs of the last segment in Falxmon serratus 

 in the form of small movable points. 



The attempt has often been made to divide the body of the higher 

 Crustacea into small sections composed of equal numbers of segments, 

 these sections consisting of 3, 5 or 7 segments. None of these attempts 

 has ever met with general acceptance ; my own investigations lead me to 

 a conception which nearly approaches Van Beneden's. I assume four 

 sections of 5 segments each — the primitive body, the fore-body, the hind- 

 body, and the middle-body. The primitive body includes the segments 

 which the naupliiform larva brings with it out of the egg ; it is after- 

 wards divided, by the younger sections which become developed in its 

 middle, into the head and tail. To this primitive body belong the two 

 pairs of antennae, the mandibles and the caudal feet (" posterior pair of 

 pleopoda," Sp. B.). Even in the mature animal the fact that these 

 terminal sections belong to one another is sometimes betrayed by the 

 resemblance of their appendages, especially that of the outer branch of 

 the caudal feet, with the outer branch (the so-called scale) of the second 

 pair of antennaB. Like the antenna?, the caudal feet may also become 

 the bearers of high sensorial apparatus, as is shown by the ear of 

 My sis. 



The sequence of the sections of the body in order of time seems 

 originally to have been, that first the fore-body, then the hind-body, and 

 finally the middle-body was formed. The fore-body appears, in the 

 adult animal, to be entirely or partially amalgamated with the head ; 

 its appendages (siagonopoda Westw.) are all or in part serviceable for 

 the reception of food, and generally sharply distinguished from those of 

 the following group. The segments of the middle-body seem always 



