1897.] NEW YORK ACADEMY OF SCIENCES. 217 



III. Hetergnereis (epitocous) and Nereis forms. 



The terms Heteronereis and Nereis have been used to ex- 

 press external morphological differences between the sexually 

 mature and immature Nereid forms. Ehlers used instead the 

 terms " epitoka and atoka distinguishing forms which bear eggs 

 (or sperm) from those which do not. The two sets of terms are 

 not synonomous as has been pointed out by Benham,* since the 

 immature form (Nereis) ma}' bear eggs or the mature form 

 (Heteronereis) be found with immature eggs. The development 

 of this knowledge by Claparede and Wistinghausen, necessitates 

 our using the older and more familiar terms to designate the 

 different structural forms, and likewise to restricting the terms 

 epitocous and atocous so as to be descriptive of the condition 

 of the reproductive organs alone. This nomenclature is used by 

 me in the following description for the sake of simplicity and 

 convenience. 



The following types of Nereis cyclurus have been found in 

 Fterenotus, Fisus, and small Natica shells. 



a. Atocous Nereis forms, two to four inches long, superior upper lohes only 

 slightly enlarged. Plate XVII., figs 4, 5, 6 ;— developes into : 



b. Epitocous Nereis form. Four to five inches long, carries eggs. Region 

 posterior to 30th segment unpigmented. In this portion, superior lobe of 

 upper part foot very strongly developed, that of 50th somite over twice 

 as large as that of 15th appendage. Eggs not found in parapods. All females. 

 Plate XVII., figs. 1, 2, 3; — probably developes into : 



c. Epitocous Heteronereis form. Has accessory foliaceous appendages to dorsal 

 cirrus and neuropodium. Body has modified appendages from 25th or 30th 

 somite back. Upper superior lobe 50th not twice as large as that of 15th, 

 i. e., anterior appendages larger relatively than in i. Parapods and body 

 distended with enclosed eggs. Plate XVIII., figs. 1-5. 



Up to the present time we have not met with a male Nereid 

 of this species. Furthermore, every specimen of types b and c 

 have been females, so that whether type a are young females or 

 undifferentiated as to sex, it seems not improbable that the males 

 may be found free-living. Although our evidence is not full 

 enough on this point to be conclusive, yet we have examined 

 some twenty or thirty specimens with the above results. 



Two very significant facts appear from a careful review of 

 Wiren's paper. (1) No male Nereis fucata ,3 inquilina (the 

 variety which lives in snail shells) has ever been found. After 

 the work upon Nereis dumerillii in which two female Hetero- 

 nereis forms occur, one at the surface and one at the bottom, 

 while the only male epitocous form is pelagic, we have precedent 

 for supposing that the male epitocous form of N. f. ,3 inquilina 



* Cambridge Natural History. 



