REMARKABLE SPECIES OF ECTTTÜROIDS. '^5 



Noteworthy is the f;ict that in Specimen A, the first pair 

 of segmental organs lies just beliind the ventral hooks ; whereas 

 in all the other specimens I have found it situated in front of 

 the hooks. It seems then assumable that the pair which pre- 

 sents itself as the first and the anteriormost in some individuals 

 is entirely lost in others. In this respect, Specimen B may be 

 considered to represent in a way a stage in which the pair in 

 front of the ventral hooks is on the way of disappearing, that 

 pair in the said specimen being represented by a single segmental 

 organ on the left but by none on the right side. This way of 

 looking at things leads one further to infer that the posteriormost 

 pair is also disappearing ; the process seems to stand on the way 

 of progress in Specimen A, and to be consummated in Specimen 

 D, as will be clear from a comparison of the above tables referring 

 to the specimens in question. Granting that the segmental organs 

 in the present species show signs of having undergone numerical 

 diminution, it may be admissible to assume that the state of 

 their pairwise or pseudo-pairwise arrangement has been derived 

 from the condition obtaining in Th. tœnioides, in which the 

 organs in question occur crowded together without apparent order. 

 In support of this view may be adduced the fact that whenever 

 more than one segmental organs from a half-pair group in the 

 present species, they are grouped together without a definite rule 

 as to their relative position. Anyway, with respect to the number 

 and the mode of arrangement of segmental organs, the present 

 species may be said to stand in a measure intermediate between 

 Th. tœnioides and other Echiuroids with only 1-3 pairs of that 



