Analysis of Heteeogeneity in Some Simplest Chakactees 313 



special cases, of a highly specialized pattern, and are through " organic correla- 

 tion " bound together, so that all show essentially the same action, even though 

 they are diverse ; and in order to meet this situation as well as one can, I have 

 investigated simplest characters in the young, also structural and physiological 

 characters. 



IN THE YOUNG. 



The young stages of these animals possess many characteristics that might 

 be made the basis of studies of simplest characters. A good example of a 

 simplest character in the larva are the spiracula spots arranged on the pleurae in 

 a single longitudinal row sujrounding the openings of the spiracles. In all the 

 chr}'somelid larvas that I have seen this row of spots is always, if present, found 

 as single indivisible pigmented areas about the spiracular openings. They are 

 never, as far as I have been able to observe in nature or produce in experiment, 

 broken into two or more elemental areas or components of any sort, and as far as 

 evidence is available they are simplest characters arranged in segmental series 

 upon the abdominal segments. They may be absent or they may be removed by 

 experimental means, especially by combined selection and environmental influ- 

 ences ; and in this instance the presence of spots is dominant over the absence of 

 them in races created by this means. Never is there any trace of a division into 

 elements, so that they are to be regarded as simplest characters. In the majority 

 of the species in this genus the spots are small, rounded, rather uniform in size, 

 presenting little in the way of variability in exposed area on corresponding seg- 

 ments in a series of several hundred individuals. Reference to the figures given 

 in this work at a different place for divers purposes will show that the character 

 in question is extremely uniform for all, and that there is little range in size or 

 shape in the segmental series or in the genus as a whole. Long ago, in a fit of 

 biometric enthusiasm, I measured the spots from camera outlines made from 100 

 larvas of L. decemlineata. Those from corresponding segments were seriated, 

 and the whole series showed only the expected monotonous array of uniform 

 steep-sided curves, all much alike in limits, identical in form, and only signifi- 

 cant of uselessly expended time and energy. 



When one searches for directions of combination with other spots, there too 

 the quest is not productive of any certain results in the larger part of the forms 

 examined. In L. diversa and L. signaticollis, however, there exists precise and 

 distinct lines of fusion, and once one knows the position of these, it is recognized 

 that the rather squared form of the dorsal edge of the spots that is often present 

 has a meaning. In the two species mentioned, the top of the spot is squared, and 

 from the anterior and posterior sides thereof there are locations and directions 

 of pigment production medianward and that may unite with corresponding lat- 

 eralward developments of the lateral tergal spots, fusing to give a U-shaped spot 

 with a heavy base and the arms reaching dorsalward towards the middle tergals, 

 with which fusion is not infrequently effected. In figure 29 I have shown some of 

 the conditions in this spot that are found in L. signaticollis. In other species 

 there is shown only an aborted attempt to develop pigment in these locations and 

 directions. 



In L. undecimlineata even this aborted tendency is absent; the spot is nearly 

 round, and when crosses are made of these two species some interesting results 



