230 "Journal of Comparative Neurology and Psychology. 



Before we state the next case, one consideration must be noted. 

 In the previous pages, use has been made of such terms as "third- 

 day," "seventh-day," and "eighth-day" larvae, to distinguish 

 the age, and roughly the stage, of certain groups of lobsters. 

 Because of the use of these terms, it must not be supposed that 

 there is aWays a constant relation betw^een the age and the stage 

 of the larvae. Among the larvae of a single group which have been 

 hatched and have developed under similar conditions, a fairly 

 constant relation between the age and stage is invariably main- 

 tained. But for different groups of larvae, this correlation does 

 not necessarily exist, for it is entirely possible, and indeed it very 

 frequently happens, that a group of seventh-day larvae may be in 

 the third stage, while a lot of eight-day individuals are in the sec- 

 ond stage. The differences in rate of development are due to 

 such factors as water density, temperature, food-supply, and con- 

 ditions of light and darkness, which, as the writer has shown 

 (Hadley '06b), may act either directly upon the body processes, 

 or indirectly by favoring or preventing the growth of various 

 body parasites such as diatoms, protozoa, and algae that naturally 

 develop in profusion on the bodies of the young larvae. This 

 explanation will perhaps make clear w^hy, in the following case, 

 we apparently retrace our steps to consider the case of seventh- 

 day larvae. In point of fact, these larvae were, at the time of experi- 

 mentation, somewhat further developed than were the eighth-day 

 larvae mentioned in Case i. 



Case 2 — July 20, 9 a.m. Twenty seventh-day larvae (eight 

 second-stage, twelve third-stage) were removed from the hatch- 

 ing bag, put in the glass jar, placed in the dark box and illumi- 

 nated by the light through the three by one inch window. After 

 a half hour, observation showed that the larvae were equally 

 divided between the window side and the room side of the jar. 

 After five minutes' exposure to red light, thirteen larvcE were posi- 

 tive and seven were negative. When, however, the amount of 

 light was increased by opening the large three by three inch win- 

 dow, only three larvae remained positive while seventeen became 

 negative. This proportionate reaction endured for several hours, 

 or until observation ceased. 



Case J— July 20, 8 p.m. Twenty seventh-day, early third- 

 stage larvae were taken from one of the hatching bags, placed in 

 the glass jar, and illuminated by an acetylene light. A more or 



