CRUSTACEAN LEG SEGMENTS — CARl'ENTIER & CARLET IO3 



The "trochanteral" characteristics of the basipodite are particularly 

 clear-cut in the Penaeids (figs. 2 and 4), primitive decapods. In each 

 of the thoracic legs of a Penaciis ^ the proximal end of the basipo- 

 dite forms with the preceding segment a typically trochantero-coxal 

 articulation ; this end of the basipodite is obliquely cut and bears two 

 tendons. These tendons are opposite each other, and one of them bears 

 a depressor muscle arising from the notal region. There is another 

 similarity with the insects (fig. 4) : beneath the tendon of the depres- 

 sor muscle, a muscle (bp-ca) is attached on the wall of the basipodite 

 of Pcnacus; it runs along the ischiopodite and the meropodite to be 

 eventually inserted on the proximal extremity of the carpopodite,^" 

 which is known to be homologous with the insect tibia. A similar 

 tibio-trochanteral muscle can be found in the insects, Periplaneta " 

 for instance. The facts we have just mentioned fit in with a homol- 

 ogization of the basipodite with the trochanter, a conception which, 

 as we saw, has already been accepted by a numl)er of authors but 

 which it was useful to buttress with further arguments. ^^ 



PLEURAL CHARACTERISTICS OF THE PRECOXOPODITE 



Thus the so-called coxopodite of Anaspides is actually a free pre- 

 coxopodite, and this precoxopodite must correspond to the pleuron 

 or to a part of the insect pleuron. Now let us see whether the malacos- 

 tracan precoxopodite actually shows, especially on the inner side, at 

 least some of the characteristics of a pleuron. We shall check, this 

 time beginning with Pcnaeus, the precoxopodite of which, like an 

 insect pleuron, has become a part of the lateral wall of the thoracic 

 segments. We know ^^ how this may have happened. The cylindrical 



9 Penaeus caramote Risso of the Mediterranean. 



10 Hinton (1956, p. 11) wrongly denies the existence of this muscle in 

 Crustacea. 



1^ Original observation. Carbonell (1947) does not figure this muscle. 



12 Then the stylus on the coxa of the Machilidae cannot be homologous with 

 an exopod. Besides it is attached rather distally on the posterior side of the 

 coxa. This stylus is probably homologous with the epipodite which we see 

 on the external side of the coxopodite of the penaeids and other Malacostraca. 



^3 See Snodgrass, 1952, p. 146, fig. 41 D. The imbedding of the proximal 

 segment of the leg of the decapods in the thoracic lateral wall has long since 

 been accepted (Caiman, 1909; Hansen, 1893) after observations of Claus 

 (1885) on the shift of the pleurogills and arthrogills of Pcnacus toward the 

 end of the embryonic life. Yet Heegaard (i947, P- 192) made certain reserva- 

 tions about those observations of Claus although he never wanted to reject 

 them completely. Let us remark that elsewhere Heegaard (op. cit., p. 188) sees 

 only two segments in the sympod of the penaeids. 



/ 



