630 



RADIATA. 



TUE COMATULID^. 



Tliis family, tlio species of which are called Hair-Stars or Feather-Starti, includes a con- 

 siderable number of animals, which bear 

 a great resemblance, both in form and 

 structure, to the Eiicrinid;e. They are, 

 however, only furnished with a stalk dur- 

 ing their young state, and on arriving at 

 maturity they quit their attachment, and 

 crawl about freely at the bottom of the 

 water, in the same manner as other star- 

 fishes. The body is flattened and cov- 

 ered with separate calcareous plates; the 

 lower, or ventral surface, bears the mouth 

 and anus; and the ten slender rays are 

 often branched to such an extent as to 

 appear very numerous. These are fur- 

 nished throughout their length with slen- 

 der, jointed cirri, similar to those of the 

 Encrinidae, by the assistance of which and 

 the short ambulacra, the Hair-vStars are 

 enabled to grasp any object firmly, and 

 creep about on submarine plants with 

 great ease. 



In their young state, the Comatulce 

 greatly resemble the animals of the pre- 

 ceding family, being supported on a long 

 flexible stalk, formed of calcareous cylin- 

 ders. So close is this resemblance, that 

 when first discovered the young of the 

 Comatula was described as a Pentacri- 

 nus. These animals are tolerably numer- 

 ous in the seas of the present day, where 

 they constitute, in fact, the principal 

 representatives of their order. In the 

 earliest ages of the world, their place 



was taken by the fixed Encrinida^ ; and the free Comatula^ do not make their appearance in any 



formation earlier than the Jurassic strata. 



THE MEDUSAS HEAD PENTACRIN0S. 



Class II. SIPHONOPIIORA. 



The Siphonophora form a group of animals of which we have still much to learn before their 

 true nature and relations can be ascertained. They are divided into two orders — the Physograda 

 and Chondrograihi . 



ORDER 1. PHYSOGRADA. 



The characteristic of the animals forming this order is, that they are furnished with a vesicular 

 organ containing air, which serves as a float to buoy them up in the water. The best known 

 of this species is the Physalia Atlantica, whicli has received from sailors the name of the 

 Portuguese Man-of- War. It swims in great crowds at the surface of the water, and possesses a 

 very strong urticating or stinging power. 



