12 



SM iTHSOXlAX M ISCKLLANEOUS COI. LECTIONS 



NUE. 



8l 



responds with the prostomial and metastomial regions of the trocho- 

 phore, and includes also the next following somite, for the first an- 

 tennae, which are the appendages of the second somite of the arthro- 

 pods, are developed on the cephalic lobes of the embryo (fig. 8 B, C. 

 'D.Avt). In the insect embryo, furthermore, the region of the rudi- 

 mentary second antennal appendages, or the tritocerebral segment 

 (fig. 8 C, ///), is often incorporated into the cephalic lobes. It is 

 probable, therefore, that the very early insect embryo represents a 

 higher stage of cephalic evolution than does the annelid trochophore 



Pre 



.Pre 



-Ant 



Pre 



Pnt 



C 



Fig. 8. — Young stages of insect embryos, showing cephalic lobes, beginning 

 of segmentation, and formation of appendages. 



A, germ band of Blatclla gcnnanica on seventh day, with cephalic lobes {Pre) 

 indicated. (From Riley, 1904.) 



B, embryo of same, about nine days old, with cephalic lobes developed into 

 a distinct protocephalon (Pre), antennae (Ant) appearing, stomodeum iStotn) 

 indicated as thickening of ectoderm. (From Riley, 1904.) 



C, young embryo of Lcpisiiia, with well -developed protocephalon (Pre), 

 bearing stomodeum and rudiments of antennae, with tritocerebral segment 

 (///) closely associated with its base. (From Heymons, 1897.) 



D, embryo of BhilcUa late in tenth day, with labrum (Lm) , mouth (Mth), 

 and antennae (Ant) on protocephalon {Pre), followed by rudiments of post- 

 antennal appendages (Put), mandibles (Md), first maxillje (iMx), second 

 maxillje (jAIx), and legs (Li). (From Riley, 1904.) 



larva, in as much as it has already progressed to a point where the 

 head includes two or three of the body segments. 



The definitive head of the arthro])od may contain as many as six or 

 seven of the body segments. Before going farther in the study of 

 ]irogressive cephalization. then, it will be necessary to understand 

 something of the development and general organization of the body 

 in segmented animals. 



r>i:\EL01^MENT OF THE BODY IN SEGMENTED ANIMAL.S 



In the Annelida, the worm form is developed from that of the 

 trochophore by an elongation of the posterior part of the larval body 



