40 W. BALDWIN SPENCER. 



somewhat more closely with one another than do the male. 

 They consist of the following parts : 



a. Ovary. 



b. Oviducts. 



c. Spermathecse. 



d. Vagina (= uterus of mature form.) 



The relations and structure of these have been carefully 

 described by Leuckart; and whilst those in P. teretiusculum 

 agree in the main with the description given by him of the 

 organs in P. tsenioides, there are certain minor differences 



(a) Ovary. — In the youngest specimen investigated the 

 ovary has the form of a simple tube, the walls of which are 

 formed of a single row of cubical cells with distinct spherical 

 nuclei, there being no difference in thickness between the 

 dorsal and ventral portions. A mesentery composed of fine 

 muscle- (?) fibres and rounded cells attaches the tube to the 

 mid-dorsal line of the body-wall (fig. 57). 



Stiles^ has figured the ovary of a young form of P. probos- 

 cideum as having the dorsal wall thicker than the ventral, 

 whilst in the same form no muscle-fibres are present in the 

 mesentery. I am not perfectly sure that such are present in 

 P. teretiusculum. 



In a somewhat older specimen (fig. 44) the ovary has under- 

 gone considerable development. Instead of forming a tube 

 circular in outline it has become somewhat flattened out 

 dorso-ventrally, thus indicating clearly a dorsal and ventral 

 side with lateral portions. 



The ventral wall is still, and remains throughout life, only 

 one cell thick ; but the individual cells are now columnar, with 

 small distinct nuclei close to their outer extremities. These 

 cells extend up the ventral half of each side. The dorsal por- 

 tion of the wall lias undergone considerable changes; the 

 single layer of cells is no longer visible, but as the result of 

 fission a somewhat irregular mass of minute cells has been 

 formed, or rather the dorsal wall is now composed of a mass in 

 which very numerous small nuclei are present. 

 ' Loc. cit., Taf. viii, fig. 47. 



