Introduction to Animal Morphology. 47 



X = very numerous in species and individuals. 



r = numerous in species and individuals, m - moderate development 

 specifically and individually, f = few species. 



V = very few, and I = single species as yet loiown. 



I. If Oldhamia be a Hydrozoan. 2, Graptolitid^. 3. Mostly Rugosa. 

 4. Mostly Cystidea. 5. Mostly Crinoidea. 6. Scolithus-like burrows. 

 7. Histioderma, Arenicolitcs, known by their tracks. 8. Orthoceras, &c. 

 9 Ammonitid^. 10. Trilobitidse. ii. Conodontes, perhaps teeth of 

 Marsipobranchs. 12. Eosaurus possibly was an Ichthyopterygian. 



As the number of known species in extinct forms 

 gives only a very imperfect idea of their absolute 

 numbers existing, as the forms known are probably 

 few in comparison with those unknown, so in the 

 foregoing table I have not given numerical ratios or 

 curves, as these are, with our present data, unreliable. 



The total number of species known, as deduced 

 from this list, is 233.250, but as many new species 

 are described every year, this is a rapidly growing 

 series. Several of the series are probably under- 

 stated. 



The animal kingdom includes eight sub-kingdoms, 

 which may be grouped as follows into two series : — 



1. Protozoa, having no definite body cavity = sub-kingdom I. Protozoa. 



2. Metazoa, having a definite body cavity (Gastrula). 



Sub-series — i. Polystomata, having many apertures into the body cavity = 

 II. Poiifera. 

 ,, 2. Monostomata, having but one aperture of ingress into 



the cavity = III. Coelenterata. 



IV. Echinodermata. 

 V. Vermes. 

 VI. Mollusca. 

 VII. Arthropoda. 

 VIII. Vertebrata. 



Of these the Coelenterata and most of the Vermes 

 agree in preserving their embryonic mouth as the true 

 ingestive opening, and hence are called Archseosto- 



