I 



without a doubt live through one winter and consequently perish at the age 

 of not less than 6 to 7 months. 



The span of life of monogenetic trematodes after the death of 

 the host is generally not great. We happened to discover live worms on 

 dead fishes not later than 24 hours after the death of the host. Usually 

 monogenetic trematodes do not abandon the body of the host under any con- 

 ditions, but certain species from the skin and fins possess this capability. 

 Thus, according to our observations, many Gyrodactylus leave the fish 

 after certain periods and for IZ to 14 hours move in lively fashion along p. 81 



the bottom of the reservoir (or container, nobis ). It is possible that they 

 are not deprived of the ability to infect new individuals of the host. As re- 

 gards the survival of the worms in artificial conditions without food (in 

 salt shakers with constantly replenished and aerated water), the periods are 

 also insignificant. Bear (Bear, 18Z7) shows that Nitzschia sturionis (Abild- 

 gaard) lives not more than 24 hours; this form lived somewhat longer --up 

 to 30 hours -- in our experiments. According to Thaer (Thaer, 1850), 

 Onchocotyle appendiculata (=Squalonchocotyle species, according to present 

 nomenclature) lives in water not more than 36 hours. Capsala molae (E. 

 Blanchard) can live in water without food up to 14 days (Braun 1889-1893), 

 Diplozoon paradoxunn Nordmann from 3 to 9 days (in the last case^ by 

 being fed with fresh fish blood). Dactylogyridae, Gyrodactylidae, 



and Polystomatidae live not more than 48 hours in water (without food). 

 Usually they perish at the end of 24 hours. 



Feeding of monogenetic trematodes takes place on the body of 

 the host and at its expense. During the time of feeding, the worms custom- 

 arily attach themselves by the anterior end and less often perform scraping 

 motions. Among the majority of forms the seizure of food takes place mainly 

 with the help of the pharynx, more seldom of the buccal funnel or buccal 

 suckers. As has already been indicated, the pharynx is capable of pro- 

 truding in a manner resembling the pharynx of Turbellaria; usually it is 

 equipped with a number of powerfully developed glands which apparently 

 play a role in the preparation of food before its seizure inside the digestive 

 system. As food, monogenetic trenraatodes use epithelial cells of the cover- 

 ing of the host, secretions of the glands, and blood. Part of the species 

 feed by all, and some only by one of these types of food. For the most part 

 Dactylogyridae feed on the mucous secretions of the skin and its cells, 

 although a number of species, as for instance Dactylogyrus vastator Nybelin, 

 Tetraonchidae, Calceostomatidae , Monocotylidae , certain Tristomidae and 

 other families close to them feed preferably on the blood; Gyrodactylidae, 

 almost exclusively on mucous and epithelial cells; Polystomidae and Sphyra- 

 nuridae, mainly on the blood. Numerous highest Monogenoidea also feed 

 pre-eminently on the blood. The egestion of undigested food remnants takes place 

 also through the buccal opening and apparently after indeterminant periods 

 following reception of food. 



79 



J 



