74 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 8 



mosaic, but this "polyplacous" condition is perhaps not always an entirely 

 reliable character, as in certain species some specimens have polyplacous 

 rings, while in others the condition is little or not at all pronounced — 

 observed in Pentarncra calcigera (Stimpson). 



Stone canal and Polian vesicle. — In most Dendrochirota there is a 

 single dorsal stone canal with round or oblong head, attached to the dor- 

 sal mesentery, or free, and one or two ventral Polian vesicles. In a few 

 species, particularly among the "polychirote" forms, there are several 

 free stone canals and often a large number of Polian vesicles also. In 

 some species the Polian vesicles have been found to be branching, but in 

 most cases they are simple. 



Gonads. — Only few and scattered observations have been made on 

 the gonads in the holothurians and here also too much emphasis has been 

 laid on the size of these organs in different animals. In Stichopus japoni- 

 cus Mitsukuri observed that the sexually mature individuals, about 3 

 years old, in short time developed few long tubes of eggs and sperms, 

 which were shed, and the tubes shriveled up and new ones developed in 

 the following year. This condition is probably the typical one in the 

 aspidochirote forms. In the larger Dendrochirota it seems as if the gonad 

 tubes increase in size over a period of years. It is possible that some eggs 

 or sperms are developed before the full size of the tubes is reached. In 

 Thyone brtareus (Lesueur) it has been observed (Kille, 1939) that the 

 number of tubes increases slightly with advancing age. The increase takes 

 place in the anterior part of the gonads, while a few shriveled-up tubes 

 are found posteriorly. A similar observation has been made on Athyonid- 

 ium chilensis (Semper). Very likely smaller, immature tubes will be 

 found to be present in most Dendrochirotes, which continue their growth 

 for several years. It is also possible that some of the so-called "hermaphro- 

 ditic gonads" merely represent the mature and immature portions of a 

 unisexual gonad. In the larger species the number of tubes is large, more 

 than 100 in each tuft; in the smaller and supposedly more short-lived 

 forms the number of tubes in each tuft is low, varying between 5-20 or 

 thereabout, and no immature portion seems to be present. More observa- 

 tions are, however, needed before any definite statements can be made. 

 Microscopical characters 



The spicules in the integument, feet, introvert, and tentacles form 

 valuable characters for identification of Dendrochirota as well as most 

 other holothurians. Certain types of spicules or derivates of these occur, 

 usually together, and accompany certain anatomical features. The spicules 



