QUARTERLY CHRONICLE. 165 



consider that the tropics are very poor in Dendrochirotids ; 

 but this would be an error. These Echinoderms have not 

 yet been collected by searching out their mode of life. In 

 fact, whilst the majority of the Aspidochirotids live in the 

 shallows within the reach of travelling naturalists, the Den- 

 drochirotids of the tropics live all at a great depth, whence 

 the dredge only can gather them. A thing well worth re- 

 mai-k is, that these Holothuriae, living at great depths in the 

 Philippine ArchipeLigo, are precisely of the forms which (as 

 the Psoli, Cucumarise, and Echinocucumes) approach most 

 nearly species of the boreal zone. It may be mentioned in 

 passing, that it is in these conditions that M. Semper has 

 fished up at the Philippines a Stellerid of the genus Pteraster, 

 which he can scarcely distinguish from P. militaris of the 

 coasts of Scandinavia. 



The Aspidochirotids, or Holothurians properly so-called, as 

 well as being very numerous in species, constitute, like the 

 Synaptids and the Dendrochirotids, an extremely uniform 

 family. It has often been repeated that the inspection of a 

 single calcareous corpuscle of the skin of a Holothuria is suf- 

 ficient to permit of the determination with certainty of the 

 species to which the animal belongs. M. Semper shows, on 

 the contrary, that the majority of these corpuscles can fur- 

 nish only very, uncertain conclusions, not only as to species, 

 but also as to genus. 



M. Semper adds to his ' Monograph of the Holothurise' 

 some very curious details as to the parasites of these Echi- 

 noderms. With the exception of some little Copepods living 

 as Epizoa on different Holothurice, the Dendrochirotids ap- 

 pear to be entirely free from parasites. The singular para- 

 sites observed by M. Semper live all on the body or in the 

 interior of the Aspidochirotids. Nearly all belong to zoolo- 

 gical groups, in which parasitism is a rare exception. For 

 example, in the first place, the fishes, — Avhich belong almost 

 all to the genus Fierasfer, Quoy and Gaimard. These fishes 

 were first described by Risso, and Delle Chiaje has figured 

 the two jMediterranean species very well. Their entrance 

 into the Holothuria, as well as their exit, appears to take 

 place through the lung. M. Semper possesses the pulmo- 

 nary tree of a Holothuria, in which is lodged one of these 

 fishes, which appears to be in the act of entrance, for its 

 head is turned towards the further ramifications of the organ. 

 They appear to be true parasites, since the author has 

 always found their stomach filled up with the debris of the 

 lung of their host. Another genus of parasitic fishes of 



