286 CHILD. [VOL. I. 



in the production of this form of variation. However, the 

 position of the organs in b and c does bring to light some 

 interesting facts regarding the orientation of the organs in the 

 segment, indicating that this also is perhaps correlated with 

 the "form" of the segment. 



In the normal form of the female organs the vitellarium lies 

 more or less completely posterior to the ovary, as is clear from 

 many of the figures (see a' in segment a of this figure, for 

 instance). The seminal receptacle appears at a point separated 

 from the vitellarium by one-quarter of the circumference of 

 the ovary, i.e., about ninety degrees (note the position of rt 

 and sr in a', where they are normally situated). Now in the 

 supplementary set of organs c" , in the segment c the vitellarium 

 lies on the right side of the ovary, while the small rudimentary 

 seminal receptacle (sr) is posterior. That is, the whole set of 

 organs appears as if rotated through an angle of ninety degrees 

 from its normal position. An oviduct, if present and normally 

 oriented with respect to the ovary, etc., would lead to the 

 shaded portion of the furrow f. 



Turning now to the organs W at the left side of b, we find 

 that the parts present in this set are the same as those found 

 in c", vis., a small ovary (<?), a vitellarium (vt), and a small closed 

 seminal receptacle (sr). The orientation of this group, how- 

 ever, is different from that of c". The vitellarium, instead of 

 being in its normal position posterior to the ovary, lies at the 

 left of it, while the small seminal receptacle (sr) is anterior to 

 the ovary, instead of to the left. Here, then, the whole complex 

 appears as if rotated through an angle of ninety degrees in the 

 direction opposite to that in which the rotation of c" is con- 

 ceived as having occurred. In consequence of this position, an 

 oviduct, if present and oriented normally with respect to the 

 other organs, would, as in the case of c", open into the shaded 

 portion of the furrow f. 



Examination of the organs rb' at the right of the segment b 

 shows that the relations there are more nearly normal. The 

 vitellarium (vt) is somewhat posterior to the ovary, and the 

 seminal receptacle, sr, though somewhat more than ninety 

 degrees from the vitellarium, does extend in a nearly normal 



