\ 6 Echinoderma. 



by demi-plates. Its pedicellariae have been preserved in the fossil state 

 both tridactyle and gemmiform. 



Ddderlein (*) finds that the lateral edges of the coronal plates in certain 

 Triassic species of Cidaris are marked by a series of small ridges. These fit into 

 small pits at the outer margins of the compressed ambulacral plates, so as to con- 

 stitute a kind of articulation. A few Jurassic species show somewhat similar cha- 

 racters, while in the Cretaceous and recent Urchins the plates have smooth lateral 

 faces at right angles to their outer surfaces, and in the oldest Urchins there is a 

 complete overlap. 



Ddderlein ( 2 j gives a detailed account of the characters of young Cidaridae, and 

 of the modifications which appear during growth in the various parts of the test. 

 He also describes 3 chief types of pedicellariae, and points out that these 

 organs furnish excellent specific characters , but have little further value for 

 systematic purposes. The earliest representative of the family is the Permian Eoci- 

 daris. The Triassic species had a kind of articulation between, the ambulacral and 

 interambulacral plates which disappears in the upper Jurassic forms. Two series 

 became differentiated during Jurassic time, those with, and those without linked 

 pores. Ontogenetically the latter condition seems the more primitive, and occurs 

 in all the Triassic species (with one possible exception). 



Kolesch has investigated numerous fragments of the Permian Eocidaris keyser- 

 lingi, and concludes that it is a Euechinoid and not a Palechinoid as supposed by 

 Zittel and others; for there are but two rows of interambulacral plates, with 6 or 

 perhaps 7 plates in a row. As these rows are meridional, Eocidaris would seem 

 to be a regular Urchin. 



VI. Holothurioidea. 



See also Semon( 1 ), supra, p 4; for the colours oiHolothuria scabra and botellus 

 see Krnkenberg( 1 ), infra, Allg. Biol. 



Bell (!) gives a popular account of the structure of Holothurians. 



Semon (*) remarks how the tendency of Sy nap (a inhaerens and digitata to imitate 

 the colouring of the sea-bottom indicates that they spend a part of their life on 

 and not in the sand. The power of loosening the attachment of the body by the 

 calcareous armature is probably due to a secretion of mucus by the integument. 

 The respiratory function of the tentacles is most important, while they also serve 

 for digging, locomotion and the capture of food particles. 



Semon ( 2 ) further points out that the radial and interradial pieces in the cal- 

 careous ring of Chirodota venusla are precisely similar. The primary function 

 of the ring is to support the tentacles and its relations to the nerves are of a 

 secondary character. The radial nerves are marked by 3 lines along which 

 the envelope of supporting cells projects somewhat inwards ; 2 of these are lateral 

 and external, and the third median and internal, while its supporting cells are 

 separated from the nerve-fibrils by a transverse cellular partition. The support- 

 ing fibres radiate through the nerve from each of these lines. Baur's vesicles 

 are not larval organs as supposed by Hamann, but otocysts, and their contents 

 are large vacuolated cells. Nerve fibres enter their walls from the radial nerves, 

 and the inner epithelium is probably ciliated. The ciliated funnels of the body- 

 cavity are large lymph-stomata which take up the granular phagocytes or 

 plasma wander-cells of the coelom, and pass them into the lacunae of the con- 

 nective tissue. These differ from the true blood-cells which have clear and non- 

 granular protoplasm, but intermediate stages are abundant. 



Herouardf 1 ) finds that the original form of the calcareous corpuscles in 





