THE APODOTJS HOLOTHUEIANS 19 



colored bodies in the skin very numerous and deep red or brown, and, with one 

 exception, no anchors or rosettes. The specimens intermediate in size differ 

 greatly in the texture of the skin, in the quantity and shade of the colored 

 bodies, and in the presence, number, and condition of the rosettes. As a rule, 

 it is undoubtedly true that the larger the specimen, the thicker the skin, the 

 fewer and more imperfect the rosettes, and the darker and more numerous the 

 colored bodies. But there are many exceptions : some rather small specimens 

 show no trace of the rosettes, while some large specimens have the rosettes 

 quite common and occasionally nearly complete. It is noticeable that as the 

 rosettes begin to disappear, the number of rods become reduced and they begin 

 to be transformed into colored bodies. Theel ('86a), Ludwig ('94), and others 

 have referred to this transformation of calcareous particles into colored bodies, 

 but in the specimens of intermedium before me, it is unusually well shown by 

 the racquet-shaped rods. The gradual disintegration of a complete rosette 

 with anchor into a heap of rounded colored bodies can be easily traced, and is 

 well shown in figures 5 to 12, Plate XII. Ludwig ( '94) in his account of T. in- 

 termedium refers to the occasional presence of peculiar, scattered, racquet- 

 shaped rods, and figures one; so that it is clear his experience was not greatly 

 different from mine. Moreover, in speaking of Ankyroderma danielsseni, Lud- 

 wig ('94, pp. 164-170) refers to the difficulty of deciding without very careful 

 examination whether a given specimen is an Ankyroderma or a Trochostoma, so 

 rare are the rosettes and anchors in some cases. As to the significance of these 

 facts, our knowledge is as yet too imperfect to draw any clear conclusions. 

 Chemical analysis of the deposits (see page 143) shows that the colored bodies 

 are radically different from the ordinary deposits in the skin. Both are possi- 

 bly connected with the process of excretion; but why one should replace the 

 other, it is certainly hard to say. That the change is closely connected with the 

 age of the individual seems to me almost certain, though it must be remem- 

 bered that size in Echinoderms is not a sure criterion of age. It is interesting 

 to note that most of the species of Ankyroderma described have been less than 

 60 mm. long, while many of the Trochostomas range over 75. The discovery 

 that the presence of anchors and rosettes is not a constant feature of even a 

 given species, combined with the fact that in Trochostoma the calcareous plates 

 and tables are more variable and show greater individual diversity than in any 

 other genus of holothurians, makes the proper classification of the genus at the 

 present time almost hopeless. There may be some species in which the anchors 

 are present throughout life and there may be species in which they are never 

 present. In determining species, therefore, the presence or absence of anchors 

 and rosettes can only be considered as a secondary character, even if it can 

 wisely be taken into account at all. The name Trochostoma antedates Ankyro- 

 derma by two years and must therefore have the preference if either be used, but 



