PREFACE. 



In offering the second volume of these lectures,^ it may be 

 well to remind the reader who may not be acquainted with the 

 Laboratory, that only 07ie side of our work is here represented. 

 Such a series of lectures on special problems in biology is 

 offered every summer; but the main body of our lectures 

 is of quite a different type, having direct reference to the 

 instruction going on in the laboratories. As a rule, these 

 special lectures are given by investigators, who undertake not 

 only to reviciv the field, but also to set forth the results of their 

 own ivork. While these lectures may show the general drift 

 of the authors' investigations, they cannot, of course, be ex- 

 pected to give a complete account of the facts on which the 

 conclusions are based. In lectures of this kind due allowance 

 must be made for the authors' limitations in time, as the sub- 

 ject is often one which would require a dozen or more lectures 

 for its complete elaboration. Somewhat greater freedom in the 

 expression of opinion than might be expected in strictly scientific 

 communications, must also be permitted. In fact, it is one of 

 the leading objects of this course of lectures to bring forward the 

 misettled problems of the day, and to discuss them freely. It is 

 to be expected, of course, that now and then opposed stand- 

 points will be developed, as has happened this time; but these 

 differences exist, and will continue to exist, as long as anything 

 remains for investigation, and the scientific reader will not be 

 surprised to find them here. It may be hardly necessary to 

 add that the authors are severally responsible for the method 

 and form of their lectures. A brief account of the work and 

 aims of the Laboratory will be found in the appendix. 



C. O. Whitman. 



1 The first volume appeared in 1890. 



