Nort) ) VARIATIONS IN LIMULUS POLVPHEMUS. 21 
PaGE 
Variation in the growth force is merely a convenient term to express 
the results following indirectly from variations in internal condi- 
tions. It is not a direct expression of variation in the quantity 
of some particular kind of energized matter. Variations in the 
internal conditions produce an apparent increase, diminution or 
subdivision of the growth force, because those conditions deter- 
mine the possibilities for a longer or shorter or different sequence 
of chemical changes, that express themselves to us in change of 
POTMAGPR cassia a Cate Boao Bcf ted sa decors oh eee ee eee, 90-94 
VII. DEGENERATION AND DEATH OF LIMULUS EMBRYOS...........:.0:::c00000---- 94 
Structure and Function of the organism a resultant of (1) Produc- 
tion, (2) Specialization, (3) Longevity, (4) Death rate of cells........ 94 
Death of Limulus embryos due to a gradual reduction in numbers 
and in specialization of the constituent cells till only very few and 
very simple cells remain. These also finally disappear.................... 95 
Comparison of this kind of death with the so-called “natural death ” 
due to the impossibility of adapting new and old parts to the new 
conditions entailed! iby their own! growth. -o1.cccececccececaceseeeseeeecseveeeeeee 95 
No necessity for assuming that there is an essential difference be- 
tween body and germ cells. ‘ Mortality” is not necessarily inher- 
ent in any living organism ; it is rather the result of an imperfect 
organization in which growth, repair, and waste continually pro- 
duce new conditions unfavorable to the continuation of the same, 
and to which the organism cannot adapt itself... 96-100 
INTRODUCTION. 
Most of the material for the following paper was obtained 
during the summer of 1891 at the U. S. Fish Commission 
Laboratory at Woods Holl. The preparations and drawings 
were made during the following winter. But since then, from 
time to time, new material was obtained, till the number 
and variety of abnormal embryos at my disposal became 
very great. The principal value of the material lies in the 
large number of abnormal embryos, and in their range of 
variation, from nearly normal ones to those so modified as to 
leave a hardly recognizable being behind. To make this range 
and diversity of variation obvious, great pains were taken to 
present as large a number of surface views as possible, made 
from stained and mounted embryos. In nearly every case the 
embryos were subsequently sectioned, and used as a guide for 
the interpretation, or correction, if necessary, of the surface 
