MYZOSTOMIDA FROM THE KED SEA. 



89 



developed specimen thei-e are 40-50, roughly corresponding to 

 the number of costse whicli terminate on them. These processes 

 are, of course, cirri ; they are better developed and more regular 

 in size in some individuals than in others, but in most cases they 

 present the appearance of typical cirri only on the anterior margin 

 in front of the mouth, where the body is thinner and more delicate 

 than posteriorly. The last pair of cirri is in most cases consider- 

 ably enlarged, forming a pair of caudal appendages into which 



Text-fiff. 17. 



Myzostoma costatiim. — Sketch of a mounted specimen 2'25 mm. in length. Caucial 

 appendages are not present and the individual is abnormal in possessing oulj' 

 four parapodia and five suckers on one side of the body. 



bi^anches of the alimentary canal and uterus extend ; in some 

 individuals these appendages reach a length equal to nearly one- 

 sixth of the length of the body. The penultimate and antepen- 

 ultimate pairs of processes are frequently enlarged also, but never 

 quite to the same degree.* The shape of the posterior extremity 



* This characteristic enlargement of the posterior cirri was not described by 

 previous investigators of this species ; v. GratF's figure (7, pi. i. lig. 14 a), however, 

 shows a distinct triangular incision at the posterior end of the bodj-, indicating that 

 something of the kind occurred in the specimens examined by liim. 



