SECT. XV CLASSIFICATION OF CRUSTACEA 259 



take the Trilobite figured in Fig. ^yA, and fold the 

 ridge round the head along the dorsal middle line, the 

 face (which lies under the glabella) would come to 

 have almost exactly the position which it has in the 

 Ostracoda. 



(2) The ridgeof the head-shield is, like the ridge round 

 the head of Apus, simply a fold of the integument, and 

 contains a part of the general body cavity. Probably 

 as in Apus and Limulus, it contained the hepatic 



Fig. 59.— Diagrammatic transverse section of an Ostracod, showing the body cavity 

 continued into the valves of the shell, into which also the hepatic diverticula 

 penetrate. The closing muscles are seen to radiate from a central sinewy mass, 

 the sternal plate. /, intestine ; /, hepatic diverticula. 



diverticula of the mid-gut. In a cross section through 

 an Ostracod the observer is at once struck by the fact 

 that the space between the laminae of the shell is con- 

 siderable, and that it is a continuation of the body 

 cavity. Not only do the hepatic diverticula penetrate 

 into it, but in some genera the genital glands also 

 (Fig. 59). While this is exactly what we should 

 expect from the bending of a head-shield with a 

 pronounced frontal ridge, w^e should hardly expect to 

 find it from a bending down of a dorsal fold. 



s 2 



