BOI'Y-CAYITY II 



(e.g. J///X/.-O the tirst maxillipede is a typical biramous limb, 

 though the expanded iiathoha>e> m some forms art- 1 - 'iniiiiH r 



^ J. -^ ^ ^ 



to project ( Fig. 1, E). while the limb following, which corresponds 

 to the second maxillipede of I>ecapods. is simply a biramous 

 swimming leg. Besides this obvious conversion of a biranious 

 into a foliaceous limb, further evidence of the fundamental 

 character .if the biramous type is found, tirst. in its invariable 

 occurrence in the Xauplius stage, which does not necessaiily 

 mean that the ancestors of the Crustacea possessed this tyje 

 of limb in the adult, but which does imply that this \\\ - 

 limb was possessed at some period of life by the common 

 ancestral ( 'rustacean ; and. second, the limbs of the Trilobita. 

 _rup which probably stands near the origin of the Crustacea. 

 have been shown bv Beeeher to conform to the hiran. 







typf i Ki-\ ]. H\ Furthermore, the thoracic limbs of 3 

 an animal which combines many of the characteristics of 

 Entomostraca and Malacostraca. and is therefore considered - 

 a -primitive type, despite their flattened character, are really built 

 upon a biramous plan (Fig. 1. (>). 



In conclu-ion. we may point out that this view of the 

 Crustacean limb, as essentially a biramous struct mv. _ - with 

 the conclusion derived from our consideration of the segmenta- 

 tion of the body, and points less to the Branchiopoda a- 

 primitive Crustacea and 11: some generalised Malacostracau 



type. 



>o tar we have shortly dealt with tho- sys 5 - 



which are clearh- affected bv the metameric segmentation f the 







b uly : we must now exp<e the condition of the body-cavity 

 a -iniilar scrutiny. If we r, move the external integument of a 

 Crustacean, we find that the internal organ- < : lie in a 

 spacior,- and discrete bodv-cavitv. as is the case in tl Annelids 



1 . . 



and Vertebrates, but that they are packed together in an irregular 

 -\-iem of spaces haeiuocoel " in communication with 

 vascular system and containiiiL; blood. In the Entomo-traca and 



* 



smaller forms generally, a definite vascular -y-iem hardly exists 

 though a central heart and artery may serve to propel : ; ' ' 

 througli the irveuular lacunae ot' tin- body-tavitv: but in 

 laiver Malaco-traca a complicated system ol irteries i 



I 



present which pour the blood into fairly definitely arrai . 

 spaces surrounding the chief organs. Tl - turn t 



