433 — 



— ^iiO 



teguments of the Phi-yganeae : Rhizoclosmatium and Siphonaria, further 

 Phlyctochytrium Schenkii and the forms parasitic in Saprolegniaceae. 



I have observed that the fructification of Achlya racemosa in nature 

 only takes place in the months of March to May during which time the 

 water still is cold. The Oogonia are sitting a long time on the hyphse, 

 what can mislead to the idea that the fructification of this species lakes 

 place during the summer. 



I have studied the parasitism of Phycomycetes on certain Plankton- 

 Crustaceans : Leptodora Kindtii, Daphnia hyalina, Hyalodaphnia cucullata and 

 Bosmina Goregoni, a phenomenon first mentioned by P. E. Miiller 

 and later observed by Wesenberg-Lund. My studies are applied to 

 the lake of Fure S0 but I have also observations from other lakes : Esrom 

 S0 and Hald S0 in Jutland. 



The form parasitic in Leptodora Kindtii is Leptolegnia caudata and 

 the attack has only been observed by me in the lake of Fure S0; found 

 also in B0gholm S0 (P. E. Muller 1868). 



The attack on Leptodora takes place in the maximum period of this 

 Crustacean from medio of July to medio of September. In the year 1904 

 I observed an attack on July 22th and in 1905 on July 11th, but in 

 other years the attack was observed (Dr. Wesenberg-Lund) in the month 

 of August. In the year 1904 the disease endured the whole summer till 

 September. 1 have not observed the entrance of the mycelium rising 

 from the zoospore, but it is possible that it takes place near the oeso- 

 phagus. The mycelium interweaves the animal totally, the mother indivi- 

 dual as well as the eggs. An immense number of zoospores are produ- 

 ced, which in short time spread the disease. 



The oogonia, which occur intramatrically, are sparingly produced in 

 the last period of the disease. This disease highly reduces the number 

 of individuals of Leptodora. 



The fungus which attacks Hyalodaphnia cucullata (lake Fure S0), 

 Bosmina Goregoni (lake Fure S0), and Daphnia hyalina (lakes of Esrom 

 80 and Hald S0), is a Pythium: P. Daphnidarum mihi. 



The attack takes place in the months of July, August and Septem- 

 ber; it can be violent during one to two weeks, mostly in the first part 

 of July, the beginning period of the disease, but it can also be sporadic. 

 During the above named 3 months a violent maximum taking place, 

 the attack is sporadic in the rest of the period of the 3 Crustaceans. As 

 to the Daphniae it is the last spring generation which is first attacked. 

 In the Bosmina I have observed that zoospores penetrate the valves 

 (cf. Fig. VIII, b). 



In these forms it is in particular the eggs which are the objects of 

 the disease; but the body of the Crustacean is always attacked and the 



