SEXUAL DIMORPHISM IN NEMERTEANS. 39 



tentacles was prolonged into a slender filament. This presum- 

 ably represents merely a relaxed condition of the tentacle, for 

 Verrill ('92) describes one or two of his specimens of N. mirabilis 

 as having similar filamentous terminal portions, while in others 

 the tentacles were contracted into relatively shorter and thicker 

 appendages, as shown in Fig. I. 



Burger ('09) studied and described anatomically one specimen 

 of Nectonemertes from off the coast of Jumba, French Congo, 

 which he identified as TV. mirabilis. Finally Brinkmann ('16) 

 has described N. minima from three males and one female > 

 also collected off the west coast of Africa. 



In N. minima the tentacles are similar to those of N. mirabilis, 

 as are also those of N. pelagica (Fig. 19). All of these descrip- 

 tions, however, were made from dead or preserved specimens. 

 The appearance of the living animal in one of these forms, N- 

 mirabilis, is shown in Fig. 18. In life the tentacles are much 

 longer and more slender than they appear in the preserved 

 specimen. A comparison of Figs. 18 and 19, although repre- 

 senting different species, will indicate the change in form which 

 takes place upon the death of the animal. 



Thus far about twenty-four specimens of the seven species 

 enumerated above have been described as having tentacles, and 

 all were males. Verrill, Joubin, and Burger recognized the close 

 structural similarity between Nectonemertes and Hyalonemertes, 

 but Brinkmann ('12) was the first to suggest that they might 

 represent dimorphic forms of a single species. As the name given 

 to the male, Nectonemertes, has priority over that of the female, 

 Hyalonemertes in Verrill's work ('92), Brinkmann correctly refers 

 his species to the former genus. 



It has been mentioned that more male individuals than females 

 of the various species of this genus have been studied. For 

 example, Cravens and Heath found only males in their five 

 specimens of N. pelagica, while Foshay was sent six specimens 

 of N. japonica, which were likewise all males. Three reasons 

 for this suggest themselves. First, the tentacles of the male 

 are presumably adapted for clasping and holding the female. 

 As a result of their clinging instinct the worms hold fast to any 

 small foreign object such as a fishing line or bait or the mesh of 



