NOTES. 



391 



121 Strictly speaking, no individual is independent. Such is the division 

 of labor in a hive, that a single Bee, removed from the community, will soon 

 die, for its life is bound up with the whole. An individual repeats the type 

 of its kingdom, subkingdom, class, order, family, genus, and species, through 

 its whole line of descent. 



128 These definitions of the various groups are mainly taken from Agassiz. 

 They are not practically very useful, as they are not used by working natu- 

 ralists. The kind and degree of difference entitling a group to a particular 

 rank varies greatly with the naturalist, and the part of the Animal Kingdom 

 where the group is found. Some families of Insects are separated by gaps 

 less than those which divide genera of Mammals. 



129 The Millepore coral, so abundant in the West Indian Sea, is the work 

 of Hydroids. The surface is nearly smooth, with minute punctures. Gegen- 

 baur, Haeckel, and others hold that the Acalephs have no body-cavity at all, 

 the internal system of canals being homologous with the intestinal cavity of 

 other animals. 



130 This digestive cavity is really homologous to the proboscis of the Jelly- 

 fish, turned in. It is lined with ectoderm. The " body-cavity " is not really 

 such, but homologous to the digestive sac of the Hydra. 



131 Among the exceptions are Tttbipora, which have eight tentacles and no 

 septa, and the extinct Cyathophylla, whose septa are eight or more. 



132 The longer septa (called primary) are the older; the shorter, secondary 

 ones, are developed afterwards. As a rule, scleroderinic corals are calcare- 

 ous, and a section is star-like; the sclerobasic are horny and solid. The 

 latter are higher in rank. 



133 Some Star-fishes (Solaster) have twelve rays. In all Echinoderms, prob- 

 ably, sea-water is freely admitted into the body-cavity around the viscera. 



134 The shell is not strictly external, like the crust of a Lobster, but is 

 coated with the soft substance of the animal. 



136 Six hundred pieces have been counted in the shell alone, and twelve hun- 

 dred spines. The feet number about eighteen hundred. They can be pro- 

 truded beyond the longest spines. 



136 The classification of this edition may be compared with that of the for- 

 mer by the following table, in which the order of the groups is altered to 

 show the relation more easily : 

 Former Edition. 



Subkingdom. 



Ill 



MOLLUSCA. 



IV. 



ARTICUI.ATA. 



Class. 



4. Larnellibranchiata. 



5. Gasteropoda. 



6. Cephalopoda. 

 3. Tunicata. 



2. Brachiopoda. 



1. Polyzoa. 



r 



Annelida = 



Crustacea. 



3. Arachnida. 



4. Myriapoda. 



5. Insecta. 



