326 ORDER CHOANO-FLAGELLATA. 



this treatise. The greater number of this series were already known to the author 

 in the year 1877, and formed the subject of a communication, accompanied by an 

 extensive set of plates, read in abstract at the meeting of the Linnasan Society on 

 June 2 1 St, 1877. While, however, it was subsequently decided to reserve all com- 

 plete textual and illustrative details for primary publication in the present manual, 

 a general summary of the contents of this communication was given in three 

 articles published respectively in the ' Annals and Magazine of Natural History ' for 

 January and August 1878, and in the 'Popular Science Review' for April of the 

 same year. As an accompaniment to the article in this last-named periodical, entitled 

 " A New Field for the Microscopist," were produced furthermore two plates con- 

 taining upon a reduced scale delineations, with their technical names attached, of 

 all the newly discovered species embraced in the larger communication made to the 

 Linntean Society, so as to secure for them a priority of nomenclature pending the 

 appearance of the present treatise. Since the publication of these several papers 

 a recognition of the collared monads has been accomplished by the German 

 authorities. Professors F. Stein and O. Biitschli, the former more especially in 

 his ' Infusionsthiere,' Bd. iii. Heft i, produced in November 1878, containing 

 illustrations, of which the textual descriptions yet await publication, of some 

 half a dozen varieties distinct from those first discovered by Professor Clark, or 

 included in the author's earlier communication of the year 187 1. Biitschli's obser- 

 vations were confined to three or four specific forms identical with types pre- 

 viously examined by Professor Clark or the author. Still later, M. Charles 

 Robin, in the 'Journal de I'Anatomie et de la Physiologie ' for November 1879, 

 has placed on record the results of his investigation of the single type Codosiga 

 hotiytis, bringing to a conclusion the enumeration of the literature concerning this 

 highly interesting group of the Flagellata so far accumulated. By no one of these 

 several authorities, however, has there as yet been produced any attempt at a full 

 interpretation of the remarkable and important functional properties pertaining to 

 the delicate funnel-shaped sarcode expansion or "collar" common to all the 

 members of this organic series. By both Professor Clark and Biitschh it has been 

 maintained that an oral aperture is present, the former indicating its position as 

 within the area circumscribed by the collar, and at the base of the flagellum, while 

 Biitschli, in the case of Codosiga bofiytis, has somewhat more vaguely defined it as 

 appertaining to special vacuolar areas developed at different points of the periphery 

 external to the base of the expanded collar. The intimate correlation of this last- 

 named structure with the process of food-inception, appears to have altogether escaped 

 recognition by these investigators. 



What the precise import of the "collar" is, and in what manner it is con- 

 nected with the ingestive functions, had been ascertained by the present author so 

 far back as the year 187 1, and is indirectly referred to in the paper then com- 

 municated to the Royal Microscopical Society, already quoted. Full details, with 

 explanatory illustrations, were, however, reserved for comprehension in the more 

 exhaustive account of this remarkable group of animalcules produced six years later, 

 and were also extensively set forth, with accompanying figures, in the two articles 

 bearing upon this subject, published in the months of January and April 1878. A 

 slightly amended quotation i?i extcnso from the later of these two publications, in 

 conjunction with the coloured frontispiece of this manual, may be advantageously 

 produced on the present occasion in illustration of the structural and functional 

 properties and peculiarities of the organ now under consideration : — " Specifically, 

 this delicate hyaline organ, the ' collar,' is of such extreme tenuity, that its true form 

 and nature can be demonstrated only by a very careful adjustment of the achromatic 

 condenser or other accessory illuminating apparatus employed, and is even then 

 exhibited to greater advantage by supplying the animalcule under examination with 

 artificial food, such as carmine or indigo. Under the conditions last mentioned, it 

 will be found that the collar consists of a transparent infundibuliform film of sarcode 

 that may be protruded from and withdrawn at will into the general substance of the 

 monad's body, in the same manner as the sarcode prolongations or pseudopodia of 

 an Amceba or other Rhizopod. As in the pseudopodia of certain Rhizopods, such 



