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



significance : it would be interesting to discover to what 

 extent they are correlated. Although the Holothurian is as 

 truly actinoneural and actinangiote as any other Echiuoderm, 

 this actinism, so frequently pentameric in character, has not 

 influenced the generative system. For the moment we will 

 leave oi)en 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 imj)ress 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 Sf/napta, 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, diflicult 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 cajcal outgrowths from the procto- 

 doeum which recall the proctodoeal caica of Bonellia and other 

 Gephyrea. 



Kecent researches in the morphology of the nephrldial 

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

 of anal nephridia in Acanthodrilus inultiporus, are sufflcient 

 to justify the speculation that the Vermian ancestor of the 

 Echinoderm was provided with a diffused nephridial system, 

 of which it is justifiable to suppose part was inherited by the 

 Synaptidge 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 the body generally which may be called podia * ; so 

 far, and 2^«ce Prof. Ludwig, there is an apodous and a pedate 

 stage among Holothurians. 



* It can only be due to the unfortunate habit of \xm\^ cumbrous peri- 

 phrases that the name sugprested by Broim (' Thierroichs,' ii. p. 088) has 

 not been adopted; it is the least objectionable of any proposed name for 

 the tube-feet. 



