267] TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY 73 



In most of the specimens taken during the spring a number of eggs were 

 present. These varied in number from one to ten, and it is probable since 

 it was near the last of the winter season that in those individuals carrying 

 one egg, this was the last, the others having been laid, rather than that it 

 was the first with others to develop later on. The one or two eggs always lay 

 in about the middle of the body, and where there were more, they crowded for- 

 ward toward the head, sometimes almost completely filling the whole anterior 

 half or even two-thirds. They were in two rows except in a few instances where 

 one, the oldest, occupied a position ventral to the others and nearer the sexual 

 pore. Since these were winter eggs, it was not surprising to find them with 

 very thick shells. These shells were dark brown and about one-ninth the 

 diameter of the egg in thickness, for the size of the animal these were very 

 large, measuring 80/x to llOfj. across. The yolk cells showed thru very distinctly 

 and were all of the same size. They were large and few in number, giving a 

 very different appearance than in the case of those where the yolk mass is 

 finely granular. With a strong light the nucleus was visible as a large clear 

 spot. Of the other reproductive organs, the cirrus could be made out large 

 and almost transparent in the parenchyma. It was nearly as large as the phar- 

 ynx and clearly showed the concentric layers of cells in the wall. The sexual 

 pore was guarded by a broad band of circular muscles. The testes appeared 

 large and solid. 



From the several descriptions given by different authors and in the above 

 details, it would appear that this species undergoes a greater amount of varia- 

 tion than is possible in many forms. 



Mesostoma ehrenbergii (Focke) 1836 



In Europe, Asia, Greenland, and AustraKa, as many as fifteen species be- 

 longing to the genus Mesostoma occur in great numbers thruout many very 

 widely separated regions. The general appearance of unhampered develop- 

 ment, i.e., large size, bright color, plumpness, number of eggs, etc., seems to 

 indicate that the varied conditions under which they live are perfect, in most 

 respects at least. A few species are confined to a Hmited area, but most are 

 to be found in both northern and southern lakes or streams. In the United 

 States the situation appears to be different. Hitherto the presence of a Mesos- 

 toma has been reported in only four locahties, and in two of these merely a 

 few scattering individuals were seen. In each instance Mesostoma ehrenbergii 

 was the form identified. That this species and also others of the genus may 

 be present in many places in America seems probable. The hardiness and 

 adaptabihty so evidenced in the rest of the world would indicate that these 

 forms are to be looked for here also. 



Among the twenty rhabdocoels which have appeared in Mississippi valley 

 ponds, it is thus to be expected that some Mesostoma might be present. So 

 far three species have been studied. Two of these, Mesostoma angulare and 

 Mesostoma simplex are new and different from the old world types. Another, 



