i;8 



THE NEMERTINI 



the posterior part is termed the "canal"; this dilates to form (2) 

 a "reservoir" or bladder, which communicates with the anterior 

 chamber by means of (3) the "ductus ejaculatorius," which traverses 

 the " diaphragm " or anterior part of the middle region. On the 

 anterior face of this diaphragm are set the "stylets"; these are 

 solid, calcareous spines (containing organic matter), generally 

 shaped like a tin-tack; of these, one is median and fixed at 

 the bottom of a funnel-shaped depression, by a somewhat conical, 

 granular mass, formed by the secretion of gland cells in the 

 diaphragm ; this is the " basis " or " acanthophore." On each side 

 of this median stylet (Begriffstilet, of Burger) is a small sac contain- 

 ing two or more lateral stylets, differing from the median one in the 

 absence of the acanthophore, and somewhat also in size (Fig. XVL). 

 In Amphiporus, alone, are there more than two 

 sacs of lateral or accessory stylets ; in this genus 

 five, or seven, or even twenty-two sacs may be 

 present. Each sac of lateral stylets opens into 

 the anterior proboscis cavity by a short duct. 

 According to Burger, each of these sacs is an 

 enormous cell, in which one or more calcareous 

 stylets arise in vacuoles each commencing as a 

 small spicule and soon attaining its full size. 

 These cells (or sacs) may be termed "acantho- 

 cysts," and each is comparable to a " rhabdite 

 cell " or " sagittocyst," from which they may pos- 

 sibly be descended. It is supposed that these 



' i 



(from joubin, lateral or reserve stylets are destined to take the 

 * r a M SeS me 8 ?y. place of the median one when (and if) this be 



stylet*' " mCdian to^ 1 



This arrangement of stylets obtains in all the 

 armed Metanemertines with the solitary exception of Drepano- 

 phorus (Fig. XVIL). Here the " acanthophore " is a long, narrow, 

 curved plate bearing as many as twenty short, conical stylets 

 arranged in a row, so that the apparatus appears to be used 

 rather as a rasp than as a dart or spearhead. On each side 

 is a number of acanthocysts, each with several accessory stylets. 



The length of the proboscis is of no systematic importance, 

 for in some of the longer forms, such as Carinella, Lineus, Eupolia, 

 Eunemertes, it is very short ; whereas, in other cases, either 

 longer or shorter worms like Cerebratulus and Amphiporus, it may 

 be actually longer than the body. The exact use of this pro- 



u*. *r A j,- 



Stylets of Ampni- 



1 According to Montgomery (30), who follows Keferstein, they are complemental ; 

 he argues against the possibility of their transference and fixation in the funnel ; 

 his account of the structure of the sacs differs considerably from Burger's, for he 

 describes an epithelium round each sac, which is a pouching of the wall of the pro- 

 boscis cavity. 



