NOTES ON THE DEVELOPMENT OF MONADIDEA. 



Hv Ar];Ri:Y ii. drew. 



Biology is as profoundly concerned with the 

 study of the smallest, as with that of the largest 

 organisms, but the class Mastigophora deserves 

 special attention from microscopists for many 

 reason;. The discovery of the Trypanosomes, and 

 their intimate relation to sleeping sickness and 

 many other diseases peculiar to tropical regions, has 

 concentrated a considerable amount of attention on 

 the Try[)anomorphidae, and numerous biologists are 

 engaged in all parts of the world in working out 

 their life-histories. The order Monadidea, which 

 comprises the least differentiated forms of the 

 Mastigophora, is well worth}- of careful inquiry, as, 

 although at present none of this order have been 

 demonstrated to be the causative agents in disease, 

 yet they are allied to the Tr\panosomes, and in 

 them we have a type of organism which is on the 

 very fringe of organised life. The opportunities for 

 discovering new and interesting forms are great, as 

 the order has been verv much neglected, and com- 

 paratively few of the organisms have been figured 

 and described. Moreover, it is extremelv desirable 

 that we should possess a full knowledge of the life 

 cvcles of the Protozoa, and an excellent held is open 

 in this direction to microscopists. It is not difficult, 

 I think, to understand why this order has been so 

 much neglected, as the organisms comprised therein 

 are exceedingly minute and consequently escape the 

 notice of the average amateur microscopist, unless 

 he is provided with first class and high powered 

 lenses. The professional worker is usuallv so taken 

 up with organisms such as the bacteria that, even if 

 he comes across the monads in the course of his 

 researches, he has no time to spare for organisms 

 that are not yet definitely connected with disease. 



.\gain. to acquire any real knowledge of the 

 development of these minute forms, it is necessary 

 to spend long and wearisome hours of constant 

 observation at the microscope, and the majority of 

 workers prefer a study that does not tax their 

 patience to the uttermost. It is, however, to the 

 amateur, who has alreadv done veoman service to 

 microscopic science, that we must look to work out 

 these organisms, and with such a wide and little 

 explored field before them it is much to be hoped 

 that ere long our knowledge of these organisms and 

 their wonderful life cycles will have greatly advanced. 

 The Monads are universally distributed in water 

 containing decomposing organic matter, either 

 animal or vegetable. They are colourless flagellata, 

 with from one to an indefinite number of flagella. 

 and a single nucleus ; the\- also possess a simple 

 vacuole system. 



Methods, of Nutrition. 

 The nutrition of the order may be holozoic, 

 saprophytic, or parasitic, but probably never 



holophytic. Formerly, the Monads were regarded 

 as essentially saprophytes, but increased knowledge 

 of the order, and particularly a careful study of their 

 life histories, has shown that almost invariably a 

 certain amount of holozoic nutrition takes place at 

 some period in the organism's development. In 

 certain forms holozoic nutrition plays a very import- 

 ant part, saprophytism being reduced to a minimum. 

 In the new monad, Moiias sarcophaga, described 

 by myself in " Knowi.kdge '" in November. 1910, 

 holozoic nutrition is bv far the most important 

 means of obtaining food, and in this particular form 

 the organism even goes so far as cannibalism. 

 Some forms, and perhaps all, in a greater or less 

 degree, are saprophytic, obtaining their nutrition from 

 the water in which thev live b\' absorbing the 

 soluble disintegration products from the breaking 

 down of complex protoplasmic molecules by bacteria. 

 The food in these cases is predigested by the 

 enzvmes secreted In- the various bacteria present. 

 Most forms, however, combine a certain amount of 

 holozoic nutrition with the saprophitic, these 

 organisms being conveniently designated as Mixo- 

 trophic. With regard to these mixotrophic forms, 

 bacteria and small protoplasmic particles, both 

 animal and vegetable, form the food, whilst in the 

 Monas sarcophaga other monads of the same or 

 different species are ingested. 



Kefkoductiox. 

 Two methods of reproduction occur in the 

 Monadidea, a sexual and an asexual. .As is the rule 

 amongst the Protozoa, reproduction by fission is the 

 commonest. Some appear to divide into many 

 smaller forms, as first recorded by the late Dr. 

 Dallinger. The nucleus in all cases appears to go 

 through a karyokinetic process prior to division. 

 This asexual process, however, does not appear to be 

 capable of maintaining the perpetuation of the 

 organisms indefinitely, and in probably all cases an 

 anisogamic method of reproduction also occurs. 

 This is almost always obscure, and can only be 

 observed by continuous and repeated observation of 

 the same form over a length of time. Dallinger 

 recorded that he and Drysdale observed the same 

 form continuously for five days before seeing any 

 other method of reproduction than the asexual. In 

 man\-, and possibly all cases, the spores which are 

 formed in this method of reproduction appear to be 

 more resistant to heat and other unfavourable 

 conditions than are the parent forms, thus tending 

 to keep the species from extinction. Dallinger and 

 Drvsdale recorded that in one form they studied, the 

 parent organisms had a thermal death point of about 

 60''C, while the spores from the sac did not perish 

 till a temperature of 149"C was reached. I have 

 found also, in the case of the Monas sarcophaga, that 



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