[Illustration: 1, _Collembola_; 2, _Thysanura_; 3, _Orthoptera_; 4, _Thysanoptera_; 5, _Hemiptera_; 6, _Lepidoptera_; 7, _Coleoptera_; 8, _Diptera_; 9, _Hymenoptera_; 10, _Diplopoda_; 11, _Chilopoda_; 12, _Areinida_; 13, _Acarina_. FIG. 22.--Number of species of different orders of invertebrates present in the manured and unmanured (or control) plots at Rothamsted. (From Morris, “Annals of Applied Biology,” vol. ix., nos. 3 and 4, Cambridge University Press.)] In point of view of number of species present (Fig. 22), _Coleoptera_ take the front rank; in the unmanured plot they are very closely approached by _Collembola_ and _Diptera_. Passing from the insects, the next assemblage of organisms in point of number of individuals are the smaller worms. The difficulties attending the specific identification of these organisms are great, and, in the present survey, the _Nematodes_ and all the smaller _Oligochætes_ have not been separated. The abundance of the _Myriapoda_ is mainly due to the prevalence of _Diplopoda_, which are represented by four species. The _Chilopoda_ almost entirely consist of a single species _Geophilus longicornis_. The dominant group of the _Arachnida_ is the _Acarine_ family _Gamascidæ_, which are represented by about a dozen species. +---------+-------------+-------------+------------+--------------+ | |Phytophagous.|Saprophagous.|Carnivorous.|Heterophagous.| +---------+-------------+-------------+------------+--------------+ |Unmanured| | | | | |plot | 14 | 48 | 13 | 20 | |Manured | | | | | |plot | 13 | 58 | 9 | 20 | +---------+-------------+-------------+------------+--------------+ CLASSIFICATION OF SOIL INVERTEBRATES ACCORDING TO FEEDING HABITS. From the point of view of the fauna as a whole, the zoological classification of the soil invertebrates is only significant when the various groups are analysed according to the feeding habits of their members. All animals are directly or indirectly dependent upon plant life for their nutrition. For the present purpose they are divided into four categories, and the position of each class of animals in the scheme is based upon the habits of its chief representatives in the soil. Definite information on this subject, however, is not always forthcoming, and it is only possible to achieve approximate estimates. In the table above the percentages in number of individuals present in the two plots investigated at Rothamsted are given under each type of feeding habit.