138 



SCIENCE. 



[N. S. Vol. XXII. No. 553. 



editions, of which the third has appeared in 

 an English translation, but differs in the 

 greater detail and precision with which the 

 various stages are defined. 



It starts with the Monera, non-nucleated 

 masses of protoplasm which ' stand exactly at 

 the limit between the organic and the inor- 

 ganic worlds ' and have originated by spon- 

 taneous generation. Of these, two varieties 

 existed, differing in their physiological ac- 

 tivities; the one group, the phytomonera, be- 

 ing plasmodomous, building up protoplasm 

 from unorganized material, and the other, the 

 zoomonera, being plasmophagous, finding their 

 nutrition in already organized material. The 

 phytomonera were the more primitive of the 

 two, the zoomonera arising from them by 

 metasitism or metatrophy, the reversal of the 

 mode of nutrition, a process which may have 

 occurred several times independently and 

 among cytodes as well as moners. Hence not 

 only have zoomonera been derived from phy- 

 tomonera, but nucleated unicellular plasmo- 

 phags have arisen from similar plasmodomes, 

 and so Haeckel takes as his second stage of 

 the ancestry the Algaria, represented to-day 

 by such unicellular algse as the Palmellacese. 

 From these he derives the third stage, that 

 of the Lobosa, represented by Amoeba and 

 having corresponding to it the ovum stage of 

 ontogeny. 



The line of descent is then traced through 

 the morsea, blastsea and gastrsea, familiar to 

 all readers of Haeckel's writings, and then 

 passes to the Platodaria and Platodinia, two 

 groups of turbellarian worms represented to- 

 day by the so-called Accela and the Rhabdo- 

 cosla. The ninth stage is that of the Prover- 

 malia, represented by such recent forms as the 

 Rotatoria and Gastrotricha, and presenting an 

 advance upon preceding stages in the posses- 

 sion of a body cavity and an anal aperture; 

 and to these succeed the Frontonia, a group 

 which many will regard as decidedly hetero- 

 geneous, since both the Nemerteans and the 

 Enteropneusta are regarded as being its mod- 

 ern representatives. Then follows the Pro- 

 chordonia stage, characterized by the _ posses- 

 sion of a definite notochord and branchial 



slits and by the absence of a well-defined 

 metamerism; its nearest representatives among 

 recent forms are the copelate ascidians and 

 the appendicularia larvsa. 



Haeckel thus omits metamerism as a funda- 

 mental and primitive condition whose exist- 

 ence in several groups of animals implies a 

 community of descent; for him it is merely 

 a mode of growth and as such has been inde- 

 pendently acquired in different phyla. He 

 regards the metamerism of the annelids and 

 arthropods as something quite different both 

 structurally and phylogenetically from the 

 metamerism of the vertebrates, and conse- 

 quently excludes the annelids from the line 

 of descent. 



The next stage ushers in the vertebrate 

 phylum and is that of the Prospondylia, which 

 finds its modern representative in the larval 

 Amphioxus, and then succeeds a stage corre- 

 sponding to the adult Amphioxus, then the 

 Archicrania, represented by the Ammocoetes 

 larva, and then a stage corresponding to the 

 adult cyclostome. The line then passes 

 through the Proselachii, Proganoidea and 

 Palsedipneusta, thence through the stegoceph- 

 alous Amphibia to the Proreptilia represented 

 most nearly by the modern Hatteria, and so 

 to the Monotremes, which represent the Pro- 

 mammalian stage. Then follows the Prodi- 

 delphian stage and then that of the Pro- 

 choriata or Mallotheria, represented by an 

 extinct group of placental mammals which 

 included the stem-forms of the rodents, un- 

 gulates, carnivores and primates and, perhaps, 

 finds its nearest recent representatives among 

 the Insectivora. From the older Mallotheria 

 the Prosimise are descended and of these 

 Haeckel recognizes two ancestral stages, the 

 Lemuravida and the LemUrogona, both be- 

 longing to Eocene times. Erom these the 

 Simise with a true discoidal placenta are 

 descended, but a discrepancy occurs between 

 the general text, which is identical with the 

 earlier edition in passing directly to the 

 catarrhine forms, and the table given on p. 

 551, in which the line of descent is taken 

 through primitive platyrrhines and thence 

 through the Cynopitheca. However, the 



