OLIGONEPHRIDIA 



263 



As development progresses, the inner layer divides on the medium 

 longitudinal line, leaving a space between. Almost immediately the 

 transverse divisions appear to form the mesodermal metameres. A 

 median cell strand is not present except that at the posterior end and also 



amf 



post 



ser.ceph 



Fig. 188. — Median sections of stages A-E of the viviparous Aphis pelargonii. (a) Union 

 of amnion and serosa, {am) Amnion, {am. cav) Amniotic cavity. {a?nf) Amniotic fold. 

 {antr) Anterior end of embryo, {b. cv) Primary body cavity, {fol) Follicular epithelium. 

 {post) Posterior end of embryo, {ser) Serosa, {ser. ceph) Cephalic serosa, {y) Primary 

 yolk, {y 2) Ovarian yolk, {yc) Yolk cells. {Adapted from Will.) 



for a short distance behind the head lobes at the anterior end. Between 

 the lateral bands of the inner layer there are a few cells arranged singly or 

 a few in a chain, cells that Hirschler says correspond to the median cell 

 strand of other insects. Therefore he considers them as the secondary 

 entoderm rudiments. They are found anteriorly from the stomodaeal 



