TABLE OF CONTENTS. 



of Radiates. — The great diversity of opinions among 

 naturalists respecting the relations of the lower animals 

 to one another, has ehiefiy arisen from a confusion of 

 ideas as to what constitutes affinity or analogy. ]i. 

 41-(;4. 



Section :i. The dasMis of Radiata. — There are only 

 three classes among Radiata, the Polyps, the Acalephs, 

 and the Echinoderms; and tliese are (diaracterized by 

 the {lillerent modes of execution of the plan of tlieir 

 type. p. C4-7'2. 



Section 4. MorphiAoiiij and nomcnclalurr. — Natural 

 range cjf homologies with reference to the nec-essily 

 of introducing new names wdien new ideas arc^ dis- 

 cussed, and, if possible, of estalilishing a connection be- 

 tween the nomenclature and the objects under eon- 

 sidcration. p. 73-S7. 



Section 5. luda-idmdllij und sjicdfic difcrcnce among 

 sicalrplm. — ImjMjrtauce of studying the question of 

 individuality in connection with that of the limitatidu 

 of species, p. SS-!i:i. Darwin's views on the origin 

 of species considered from tliis side of the question, 

 note p. Sfl. 



Section (">. Natund limits of the elass ef Aeedephs.-- 

 Tliongh gi-adually extended farther and farthei-, tlie 

 limits of this class have not yet been sufficiently ex- 



]iaiidi-il to include all the animals which are now 

 believed to belong to it. p. 99-113. 



Sectio.v 7. Gradation among Acalejihs. — Simple as the 

 structure of the Acalephs is, it is sufficiently compli- 

 cated readily to jioint out the relative rank of the 

 dilfereiit types belonging to the class, p. 113-124. 



Sectio.v S. Succession of Acalcjjhs. — The order of suc- 

 cession of the Acalepihs in geological times can thus 

 far only be traccil in one of their types, the Tabulata, 

 through a long series of ibrmatious. p. 12.5-129. 



Sectio.v 9. Classif cations of Acalephs. — Before the 

 beginning of tliis century, nothing was done towards 

 classifying the jVcalephs. Lamarck first unites together 

 the m.ijority of their representatives; then foUow the 

 classifications of Peron and LeSneur, of C'uvicr, of 

 Schweigger, of Goldfuss, of C'hamisso and Eysenhardt, 

 of Latreille, of Eschscholtz, of DeBlainville, of Oken, 

 of Brandt, of Lesson, of Forbes, of Liitkcn, and of 

 Jlilne-Eilwards. More recently embryological researches 

 have greatly influenced the views of naturalists re- 

 specting the affinities of the Acalephs, and there have 

 appeared new classifications ]>roposed by Vogt, Kolli- 

 ker, Lcnckart, (iegenbaur, iNIcCrady, and Huxley. 

 The stuily of the homologies is likely to modify 

 these views anew. p. 129-1J2. 



PART II. 



C T E N P 11 R yE 



C II A P T E R I . 



CTENOPIIOK^'E IN GENEPvAL. 



Section 1. Slrudural features of the Ctenojilionr in 

 general. — Special homologies traced among all Acalephs, 

 in order to show the peculiarities of the structure of 

 the Ctenopliora?. Natural attitudes and normal position 

 of the Aealeph.s. p. 155-173. 



Section 2. Sidulicisions of Ctcnojdiora' forming suli- 

 orilers. — Critical analysis of the .systematic value of 

 till' different names under which the different kinds of 

 natural groups oljserved among Acalejihs have been 

 designated, p. 174-lSG. 



