NO. 3 deichmann: holothurioidea; parti, dendrochirota 73 



number of feet increases with advancing age. Man}^ descriptions, "feet 

 in 3-4 rows," "single row, etc.," are of little value except when the ani- 

 mal is well expanded and its size also is given. In some species the feet 

 are heavily armed with spicules and unable to retract; in others equally 

 well armed they may be withdrawn. Where the feet contain few spicules, 

 the feet are often completely retractile. In younger individuals the ar- 

 rangement of the feet is often untypical, as mentioned above. 



Inner organs. — Much space has usually been devoted to the inner 

 anatomy of the Dendrochi rotes, but with the exception of the calcareous 

 ring, the stone canal, Polian vesicle, and gonads, all other organs may 

 usually be ignored. A few species are said to lack a muscle stomach, but 

 I am not sure that the observation is correct. The course of the intestine 

 and the attachments of the mesenteries to the body wall are fairly stable 

 characters, although some variation has been noted, but the contracted, 

 contorted condition wherein the material often is preserved, or the com- 

 plete loss of inner organs, makes it impossible to use these structures 

 consistently. The Cucumariidae seem typically to have the third mesen- 

 tery attached on the right side of the midventral muscle band, the Phyl- 

 lophoridae seem to have it attached to the left, and the Psolidae have it 

 either way. The thickness or thinness of the longitudinal muscles, the 

 place of attachment for the retractors, the shape of the branches of the 

 respiratorj'^ trees, et cetera, are all characters of rather dubious value and 

 the use of them has often caused misidentification. 



Calcareous ring. — The calcareous ring presents a character of utmost 

 importance, as certain types invariably seem to be combined with a cer- 

 tain arrangement of the tube feet and certain types of spicules. 



The calcareous ring is designated as simple when the radials and 

 interradials have fairly low, broad basal portions with shorter or longer 

 anteriorly projecting teeth, while the posterior margin may be almost 

 straight or undulated, sometimes with faint protuberances on the radials. 

 In the complex ring the radials have distinct posterior prolongations, the 

 so-called "tails"; and the body of the radials may be deeply cleft, some- 

 times almost to the base of the anterior tooth. In some species the tails may 

 be secondarily more or less resorbed or hidden in the tissue and hence less 

 noticeable. The interradials either are fairly broad, overlapping the ra- 

 dials as heart-shaped or diamond-shaped pieces, or are narrow, often 

 quite tall, rectangular, and firmly united with the radials; rarely are they 

 vestigial ; the anterior tooth may be short or long. The complex cal- 

 careous ring may furthermore be composed of several smaller pieces as a 



