208 Prof. F. J. Bell on the Arrangement and 



significance ; it wonkl be interesting to discover to what 

 extent they are correlated. Although the llolothurian is as 

 truly actinoneural and actinangiote as any other Echiuo lerm, 

 this actinism, so frequently pentameric in character, has not 

 influenced the generative system. For the moment we will 

 leave open the question whether this is a primitive or a secon- 

 dary character. We can well imagine that the development 

 of a calyx — early acquiring, Tiarechinus would lead us to 

 suppose, a large size, — if itself actinal in arrangement, would 

 do much to impress actinism on all the systems of the body. 



However, be that as it may, Holothurians are non-calicu- 

 late and anactinogonidiate, and so far they differ from all 

 other Echinoderms known to us. 



3. The musculature of the body-wall is well developed and 

 consists of longitudinal and circular muscles ; the latter may 

 be brought so far under the influence of actinism that they 

 are not continuous as in Si/napfa, but are broken at the rays. 



Like all other characters, this must either have been 

 inherited or secondarily acquired; we may be sure that an 

 ancestor of the Echinoderms possessed it, so that the Holo- 

 thurians have either inherited it or their ancestors lost it and 

 they reacquired it. Between these probabilities it is not, I 

 think, difficult to make a choice. 



4. There is a system of infundibular organs which it is 

 hard to imagine are not the homologues of the nephridia of 

 many Vermes. Or 



5. There is a system of ca^cal outgrowths from the procto- 

 do2um which recall the proctodoeal ca3ca of Bonellia and other 

 Gephyrea. 



Recent researches in the morphology of the nephridial 

 systems of Vermes, and especially Mr. Bcddard's discovery 

 of anal nephridia in Acanthodrilus mulliporus, are sufficient 

 to justify the speculation that the Vormian ancestor of the 

 Echinodcrm was provided with a diftused nci)hridlal system, 

 of which it is justiflable to su]ipose part was inherited by the 

 SynaptidfB and part only by the other Holothurians. 



6. The water- vascular system is always continued into 

 circumoral tentacles, but not always into those similar struc- 

 tures on tiie bofly generally which may be called podia*; so 

 far, and ^>rtfe Prof, [judwig, there is an apodous and a pedate 

 staiic anionir Holothurians. 



* It ran only bo due to tlie unfortunato habit of usin;^ cumbrous pcri- 

 phrasL's tliat the iiaiue su'rj.'-estod bv IJronn (' Tliiorroiclis,' ii. p. ."{S."}) lias 

 not boon adoptod ; it is tiie least ubjei. tionable of any proposed name for 

 the tube-foot. 



