THE APODOUS HOLOTHURIANS 143 



companied by a constant decrease in the calcareous bodies. (See an tea, p. 19.) 

 In young specimens the colored bodies, even if not wholly wanting, are often so 

 small and few that they cannot be seen without magnification ; but as the animal 

 grows they become more numerous, are collected together in groups and 

 patches, and appear to the unaided eye as spots or blotches of various shades. 

 In still older specimens these blotches tend to merge together, and gradually 

 the entire body-surface may become a uniform deep purplish red, red brown, or 

 even almost black. If calcareous deposits still persist, they will be found 

 normally outside the deeper-lying "colored bodies." In 1901 Mr. W. L. Sperry, 

 then of Olivet College, kindly undertook for me a chemical examination of these 

 colored bodies, making use of specimens of M. oolitica, intermedia, and 

 DiKsculus. Just after he had gone far enough to prove that the chemical ele- 

 ments involved were chiefly phosphoric acid and iron, Morner's (:02) paper 

 ai)i)eared with an account of his similar investigations. Mr. Sperry continued 

 his work far enough to confirm Morner's analyses; so that the composition of 

 these remarkable "colored bodies" may be considered as settled. Morner gives 

 the result of his analysis as FeP03+4 H,0=66.2, Fe(OH),=20.2 and CaC03= 

 6.4. Mr. Sperry's analysis differed from this only in a few details, the most 

 interesting of which was the probable presence of Mg. There is also reason 

 to believe that the amount of CaCOa is subject to much variation; probably 

 when calcareous particles are first transformed into the colored bodies, CaCOj 

 is the most important substance present, and as the color deepens, it decreases 

 rapidly in amount. Apparently the calcium as well as the CO2 is excreted as 

 these changes take place. In view of their remarkable composition, we are justi- 

 fied in referring to the "colored bodies" as "PHOsPHATic DEPOSITS," iu distinc- 

 tion from the "calcareous deposits" so characteristic of holothurians. The 

 presence of phosphatic deposits is limited among Echinoderms, so far as is 

 now known, to about 20 species of Molpadids, all but two of which belong to 

 the genus Molpadia. The "round" spicules with a "radiate" appearance, de- 

 scribed and figured by Danielssen and Keren ('82) in connection with their ac- 

 count of Trocliostoma thomsonii, have not been met with by other investigators, 

 and Theel ('86a) is doubtless correct in considering them as artifacts. 



3. The transverse muscles lie just beneath or within the connective-tissue 

 layer, and, unlike the arrangement in the Syuaptida>, are confined for the most 

 part to the interradial areas. The fibers are inserted in the connective tissue a 

 little to the side of each radius, and may be so few that when the animal is ex- 

 tended they do not form a continuous layer. Just behind the tentacles they are 

 more numerous, and are continuous across the radii, thus forming a circular 

 muscle which serves as a sort of anterior si)hincter when the tentacles and oral 

 disc are retracted. In Caudina and Aphelodactyla, and probably in all J\Iol- 

 padids where the connective-tissue layer is sufficiently thick, there run out into 



