COPULATION IN A TURBELLARIAN WORM. 



301 



To determine certain points relating to internal organs, serial 

 sections were made of one of the pair; fixation proved to be sat- 

 isfactory. As to the normal anatomy of the reproductive 

 organs, the description and figures given by Curtis 1 are wholly 

 adequate and correct. Naturally in the process of copulation the 

 terminal portions of the vasa deferentia become adjusted to the 

 protruded penis; and for the sake of easy comparison, Curtis's 



FIG. 4. (a) Normal resting position of the reproductive organs of Planaria 

 maculata, from lateral aspect. (After Curtis.) G.a., Genital atrium; Od., Ovi- 

 duct; Ph., Pharynx; P, Penis; U., Uterus; U.d., Uterine duct; V.d., Vas deferens. 

 (&) Same as (a), with organs in position during copulation. 



figure of the retracted arrangement of these organs is reproduced 

 beside one drawn from the same aspect with the penis in copulat- 

 ing position. No comment seems necessary by way of interpret- 

 ing these figures; in mating, the penis is turned posteriorly, 

 extended through the atriopore, and considerably enlarged. 

 This change in position tugs on the vasa deferentia (seminal 

 vesicles) and straightens out the loops which occur in them when 

 at rest. 



Concerning the place of deposition and storage of the transfer- 

 red sperm, a further word may be added. The cavity of the 



1 Curtis, W. C., Proceedings of the Boston Soc. of Nat. Hisl., Vol. 30, No. 7, 

 1902. 



