POLYCLAD FLATWORMS — HYMAN 561 



attention has been paid to the available deta,ils about the species. In 

 view of the unsatisfactory nature of some of the descriptions and the 

 failure to mention certain points, especially the presence or absence of 

 accessory prostatic vesicles and antral glands of the male apparatus, 

 it seems to me we are not in a position to declare definitelj'' that any 

 one of the species is sjaion^anous with any other. 



I am reluctant to add another species to this complicated situation 

 but I am not able to identify my form, with any of the previously de- 

 scribed species. The present specimen resembles P. oligoglena in color 

 and in the presence of two very large teeth in the cirrus sac but 

 dilTers in the fewer cerebral eyes, the cloud of black dots middorsally, 

 the entrance of the common sperm duct into the prostatic duct, not 

 into the prostatic vesicle, the poor differentiation of the tv/o accessory 

 prostatic vesicles, the extreme differentiation of the two cement 

 pouches, and the shorter Lang's vesicle. The conspicuous coils of the 

 right spermiducal vesicle in fi'ont of the biu-sa, typical of P. oligoglena, 

 are wanting. 



The cloud of black dots in the middorsal region appears to be a 

 very definite character. It can scarcely be overlooked as it is notice- 

 able at once on low magnification. These dots, as already mentioned, 

 are in the mesenchyme. They are not the same as the dots in the 

 intestinal branches mentioned by several authors. It appears that 

 such dots are recorded only for P. langi (Laidlaw) (1902) and P. 

 rotumanensis Laidlaw (1903a). P. langi is described as white, with 

 "two" cerebral ej^es, cylindrical tubular cirrus sac lined throughout 

 wath spines, short wide prostatic duct receiving the common sperm 

 duct, and two "folds" in the cirrus sac. If in fact P. langi regularly 

 has only two cerebral eyes this would differentiate it from all other 

 species of the genus. The number of cerebral eyes is of course some- 

 what variable among individuals of the same species but not to that 

 extent. It is not clear just what is meant hj the folds in the cirrus 

 sac, but apparently they are not teeth. The description of P. 

 rotumanensis is even less satisfactory. The cerebral eyes are rather 

 numerous, divided into two groups on each side, the intestine gives 

 off dorsal diverticula containing brown spots, the prostatic duct 

 enters the cirrus sac on the ventral side, the lumen of the cirrus sac 

 is lined throughout with spines, two folds like those of P. langi are 

 present, the common sperm duct enters the prostatic duct, and Lang's 

 vesible is rather large and long. It appears impossible to reconcile 

 P. fritillata with either of these descriptions. It has a fair number of 

 cerebral eyes, scarcely divided into two groups on each side, the cirrus 

 sac is thick and oval, not tubular, the prostatic duct is rather long 

 and enters the cirrus sac in the middle of its dorsal surface, the lu- 

 men of the cirrus sac rather lacks spines anteriorly, the two very large 



