378 



COMPARATIVE ANATOMY 



CHAP. 



degeneration of the parts not immediately connected with reproduction. The 

 intestine is thus wanting in the dwarf male of the Cirripedia which on reaching its 

 destination, i. e. the body of the female, there leads a semi-parasitic life. If the male 

 does not reach this destination, he has failed in his life-work and perishes. To this 

 subject of dwarf males we shall have to return (p. 382). 



The accompanying figures (Figs. 252, 253, 254) illustrate the great sexual 

 dimorphism found in certain parasitic Copepoda and Isopoda. 



(b) The olfactory filaments (Riech- und Spur- faden) on the anterior antennae are 

 always present in far greater numbers in the male than in the female. 



FIG. 253. Portunion Maenadis. Adult mature female (after Giard andBonnier). A, With the 

 brood cavity partly opened in the ventral median line and the brood lamellae'separated. The 

 abdomen (db) is so placed that the ventral side is seen. Ir, The anterior middle and posterior lobes 

 of the first brood lamella on the right side ; II, the same of the first brood lamella on the left ; II r 

 and II I, 2cl brood lamella (right and left) : Illr and III I, 3d brood lamellae (right and left) ; IV, 4th 

 brood lamellae; Vr and VI, 5th brood lamellae (right and left); pi, pleural lamella of the 1st 

 abdominal segment ; ex%, exopodite of the pleopod of the 2d abdominal segment ; en^, endopodite 

 of the pleopod of the 3d abdominal segment ; ov, ovary ; eg, cephalogaster ; ae, outer ; ai, inner 

 antennae ; mf, maxillipede. B, Adult female, brood cavity not opened. The abdomen ab is seen 

 slantingly from above ; th, thorax ; eg, cephalogaster ; Ji, cardial prominence. 



(c) In the males of the most different divisions, apart from the actual copu- 

 latory organs, there are limbs transformed into " accessory organs of copulation" 

 for the seizing, grasping, and holding fast of the female. Such are the posterior 

 antennse of Branchipus, the seizing hooks in the anterior pair of limbs of the 

 Estheridce, the adaptations for holding the female in the 2d antennse or the 

 maxillipedes of the Ostracoda, the anterior (seizing) antennse of the Copepoda, etc. 

 In the Amphipoda the seizing hooks on the anterior thoracic feet are more strongly 

 developed in the male than in the female. In the Anisopoda ( Tanais dubius) 2 forms 

 of males have been observed, both of which seem to be peculiarly well organised for 

 catching and holding the female. The one form may be called " scenters," the other 



