Inter-relations of the Classes of the Echinodermata. 209 



7. The specialized " heart," '■'■ ovoid gland," or " plexiform 

 gland " is not developed. 



This, if the Holothurians are primitive among the Echino- 

 derms, was only to be expected. 



8. The larva is simple, and, on the whole, the mode of 

 reproduction is less complicated than in other classes. 



The position, then, that the Holothurians are primitive 

 forms is spoken to (1) by the possession of characters certainly 

 possessed by its ancestor, and (2) by the absence of characters 

 seen in other Echinoderms, and evidently differentiations of 

 structures developed after the ancestor of the Echinoderm had 

 become separated from the ancestors of other phyla *. 



(b) The Relations of the remaining Echinodermata 

 among themselves. 



But while Holothurians are non-caliculate and anactino- 

 gonidial, all other Echinoderms are caliculate and all that we 

 know are actinogonidial. Considering the irregularity of the 

 actinism of some Cystids, such as, say, Atelecystis Forhesi or 

 Garyocystis^ we may reasonably suppose that some of them 

 were anactinogonidial. We have then caliculate and non- 

 caliculate groups, and of the former there were in all proba- 

 bility some that were anactinogonidial. 



The pelmatozoic condition, to which Leuckart was the first 

 to draw attention, was by him regarded as the actual or 

 potential possession of a stalk ; but this connotation has 

 become altered. By Pelmatozoa we have recently meant 



* The argument from habitat is not of itself of much value, but it may- 

 have a cumulative force, coming after those which I have already adduced ; 

 and the fact that Holothurians have been found in brackish water may 

 fairly be stated thus — they are not so differentiated as to be unable to 

 live in any medium other than salt water. The ancestors of our existing- 

 archaic forms must surely have dwelt along a shore-line such as that 

 described by Dr. von Kennel ('Arbeiten aus dem zool.-zoot. Inst, in 

 Wurzburg,' vi. p. 276) : — " In diesem Wasser nun, fiir dessen Quahtat 

 als Siisswasser ich freilich keine anderen Kriterien habe, als den Ptlanzen- 

 wuchs und das Gefiilil der Zuuge, da ich leider keine Analysen ausfiihren 

 lassen konnte, herrscht ein merkwiirdiges Thierleben. Zahllose Frosch- 

 und Krbtenlarven bedecken in schwarzen Kluinpen den Boden oder hangen 

 an den Wasserpflanzen, Unmassen von Mlickeularven verschiedener Gat- 

 tungen schwimmen theils frei, theils sitzen sie an der Unterseite dei* 

 Blatter und Steiue, dieim Wasser liegen, Libellenlarven und Wasserkafer, 

 sowie kleine Tauchwanzen, tummeln sich lebhaft herum, und mitten 

 darunter ebenso massenhaft, wenn nicht in griisserer Zahl, Mysis, Nerei- 

 den und kleine Quallen, zusammen mit Palaemoniden und eine kleine 

 Atyaart, zu schweigen von den kleinen rhabdocoelen Turbellarien, &c." 



Ann. & Mag. N. Hist. Ser. 6. Vol viii. 14 



