452 T. J. EVANS 



channel (sp.p.) is also essential for the passage of the backwardly 

 migrating spermatozoa. It is, therefore, seen that diauly of 

 the female duct in Calma is just so far expressed as to con- 

 stitute passages that are functionally efficient. 



The foregoing rather detailed account of the female reproduc- 

 tive ducts, though a digression from the main thesis of the paper, 

 has been introduced because the supposed female monauly of 

 the Aeolidiomorpha forms an important item in the definition 

 of that group. 



The reproductive system as a whole presents three anatomical 

 departures from the Aeolidian type, namely (1) the displace- 

 ment of the male opening and its accessories into the head, 



(2) the substitution for a muscular penis of one which derives 

 its bulk from a gland which grows at sexual maturity, and 



(3) the breaking up of the massive aeolidian gonad into serially 

 arranged pairs of gonadial units which are so placed as to 

 intrude least on the body-space available for distention of the 

 alimentary system. They are, moreover, placed where digestion 

 of a meal begins, and in the path of food-laden blood from the 

 cerata, so that their growth proceeds pari passu with the 

 adjacent reduction in bulk of the stomach. All three modifica- 

 tions may be regarded as correlated with the demand for space 

 to receive the maximum meal when food is plentiful. The 

 last further enables Calma to replace that meal by its own 

 enlarging gonads with the greatest structural convenience. 

 Figs. 8 and 9 are sections through the interceratal regions of 

 two animals of similar size at nearly opposite poles of the 

 metabolic cycle. In fig. 8 digestion has begun, the gonads 

 are small, and the special cells (c.s.) in the cerata are almost 

 at minimum size, while in fig. 9 the meal has largely disappeared, 

 the special cells are greatly enlarged, and the ovarian acini 

 (/.a.) are distended with nearly full-grown eggs. In this 

 specimen the black granular remains (d) of a previous meal 

 are also visible on the floor of the gastric sac. As animals of 

 various sizes are found in both of these metabolically antithetic 

 conditions, it is almost certain that the rhythmic succession 

 of alimentary and reproductive activity takes place several 

 times in the individual lifetime. Dr. Orton (8) has shown by 



