46 ILLINOIS BIOLOGICAL MONOGRAPHS [240 



the intestine are very prominent. The ovary, testes, and other accessory parts 

 are often so embedded as to be difficult to make out, but always the yolk glands 

 can be seen nearly as large as the intestine itself, extending up around it toward 

 the dorsal side. In many instances also the rather large opaque egg is evident, 

 more or less completely filling the posterior region of the body. The anterior 

 end is commonly truncate with the mouth a conspicuous hole just ventral 

 to the very front margin. The development of a tail-like portion is somewhat 

 variable but all the forms show at least a tendency in that direction. The 

 shape as a whole is much more slender than in many families. The color 

 ranges from almost black to clear transparency. The above summary mentions 

 points in the general make-up which causes this group to be one of the most 

 easily recognized of all the families. 



Dalyellia dodgei von Graff 1911 

 Figure 49 



This species was taken together with half-a-dozen other rhabdocoels from 

 a small tem.porary pond which during April was up to four feet deep but which 

 later would dry completely unless the rains were especially heavy. It drained 

 dovvoi into a little river and so was not entirely cut off from the outside. There 

 was a muddy bottom with some algae and many leaves from near-by oak 

 trees. The site was protected from, wind by hills so that the warmth of the 

 sun v/as felt early. The special locality was the surface of bottom mud or 

 a small mass of algae. Either was a good hiding place as the animal is nearly 

 black. The motions are sluggish and not constant. When at rest, the body 

 is drawn up to one-half its extended length and seems almost round. It is 

 not as easily frightened as most of the other species and when aroused more 

 quickly becomes quiet. One little habit is quite noticeable. Very often 

 when the rather small mouth is opened, the front end of the head is slightly 

 elevated to give the ventrally placed mouth cavity a more advantageous 

 position. The two corners of the head are very contractile and are used ahnost 

 like lips to guide particles of food into the opening between them. When the 

 animal is moving along, the mouth is closed and the ventral surface held down. 

 The head never turns from side to side, and the whole body is straight, keeping 

 to a rather definite course for the most part. 



This form agrees closely with that from Rochester described by von Graff. 

 He speaks of it as occurring there more frequently than almost any of the other 

 rhabdocoels. The conspicuous characters are: first, double arrangement of 

 the pharynx with its especially developed papillae; second, the mottled color 

 due to scattered pigment cells, and third, the complexity of the reproductive 

 organs. This western type is noteworthy as showing wide distribution in a 

 species found commonly in a certain restricted locality, and seems to be in- 

 dicative of its probably wide-spread occurrence. A resume of its variations 

 may be of interest. 



