154 Dr. C. A. Kofoid on Pleodorina illinoisensis. 



occurring in Pandorina and Eudorina, deserves passing 

 notice. It occurred with considerable frequency in all three 

 genera, and resulted in each case in the destruction of the 

 entire colony affected. The early stages of the disease, if it 

 be such, are indicated by the homogeneous condition of the 

 cells and the fadiug out of the colour, together with a flat- 

 tening of the cell-contents into a disk- or lozenge-shaped 

 mass (PI. V. fig. 4) . In the subsequent stages this mass 

 assumes a yellow and then a brownish colour, takes on an 

 irregular shape (PI. V. fig. 5), and disintegrates, leaving the 

 empty cell -walls occupying the matrix. In spite of the 

 suggestion in the above description there was never any trace 

 of the formation of spermatozoa in the colonies presenting 

 these phenomena, neither was there any indication of encyst- 

 ment. There was no indication of either a fungous or an 

 algal parasite, and it seems not improbable that the occur- 

 rence of these diseased forms may have been due to some 

 unfavourable local condition in the water tributary to the 

 habitat of the genera affected. 



The following brief synopsis of the prominent characters of 

 this genus and its two species will serve as a convenient 

 diagnosis for their determination : — 



Pleodorina, Shaw. 



Colony consists of a spherical or elliptical coenobium of 

 greenish biflagellate cells of two types, vegetative and 

 gonidial, in the anterior and posterior parts of the colony 

 respectively, which lie in the periphery of a hyaline gelatinous 

 matrix and are surrounded by a common hyaline envelope. 

 Cells each with one reddish stigma, which is more prominent 

 in the anterior part of the colony. No connecting filaments 

 between the cells. Non- sexual reproduction by gonidia, 

 which are formed by increase in size of a part of the cells of 

 the colony. Daughters escape from parent as small colonies 

 of biflagellate cells, which at this stage are all similar. 

 Sexual reproduction not known. 



Pleodorina californica, Shaw. 



Number of cells in colony 64 or 128. Maximum diameter 

 of colony 175-340 fx,. Vegetative cells constituting approxi- 

 mately one half the colony. Gonidial cells 2-3 times diameter 

 of vegetative cells. Known habitat : ponds, ditches, and 

 streams in California, Indiana, and Illinois. 



