Intcr-relatw/hs of tlie Classes of (he Echinodermata. 209 



7, The specialized " licart," " ovoid gland," or " plexiform 

 gland " is not developed. 



This, if the Ilolotlmiians are primitive among the Echiiio- 

 dernis, 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 llolothurians 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 develo[)ed after the ancestor of the Eciiinoderm had 

 become separated from the ancestors of other phyla *. 



(b) The Relations of the remaining Echinodermata 

 among themselves. 



But wliile llolothurians 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 Forbesi or 

 Caryocystis, 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 Pelraatozoa we have recently meant 



* The arp:ument 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 Holothuriaus have been found iu brackish water may 

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

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

 archaic forms must sm'ely have dwelt along a shore-line such as that 

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

 Wiirzburg,' vi. p. 270) : — " In dieseiu Wasser nun, ftir dessen Quahtat 

 als Slisswasser ich fi-eilich keine anderen Kriterieu habe, als den Pflanzen- 

 wuclis uud das Gefiihl der Zunge, da ich leider keine Analysen ausfiihren 

 lassen konute, herrscht ein merkwiirdiges Thierleben. Zahllose Fro^ch- 

 und Kroteularven bedecken in schwarzen Ivluuipen den Bodeu oder hangen 

 an den Wasserptlauzen, Unmassen von Miickenlarven rerschiedener Gat- 

 tungen schwimmeu theils frei, theils sitzen sie an der Unterseite der 

 Blatter und Steiue, die im Wasser liegeu, Libellenlarveu und AVasserkafer, 

 sowie kleine Tauchwanzeu, tummehi sich lebhaft herum, und mitten 

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

 den und kleine Quallen, zusammen mit Palaemoniden uud eiue kleine 

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



Ann. tf.- Mag. X. Hist, Ser. 6. Vol. viii. 14 



