GIANT LARV/E FORMATION IN ARBACIA PUNCTULATA. 27 



larvae. Atypic or incomplete larvae may be formed. I have 

 many records of the transformation of pairs of grafted gastrulae 

 into atypic enlarged or incomplete single larvae, which will be 

 described elsewhere. They are the resultant, from the present 

 evidence at least, of a disturbance in the translocation and 

 rebuilding of cells that make up the skeleton, rather than a 

 resultant of asymmetrical positions of the fused members. 



CHANGE OF AXES DURING DEVELOPMENT. 



In studying the development of fused gastrulae, it became 

 evident that in many instances the relative position of the axes 

 was definitely altered, so that the angle formed by the two guts 

 and therefore the symmetry of the two fused members, was 

 profoundly altered during development. For example, in Fig. 

 30, two nearly equal gastrulae were fused in such a manner that, 

 though their blastopores are nearly united, their guts diverged 

 about 60 degrees from each other. During the next six hours, 

 besides increasing in size, and besides an unequal growth of 

 the two guts, the relative position of the axes had shifted from 60 

 to nearly 80 degrees (Fig. 31). This double gastrula gave rise, 

 by the process of absorption, to a "single" larva, with a some- 

 what incomplete skeleton and single gut (Fig. 32). 



Fig. 33 is a drawing of two fused gastrulae twenty-four hours 

 after fertilization. One member has its gut fully formed, the 

 other member has just begun to differentiate it. Their axes 

 are about 90 degrees apart. During the next seven hours two 

 changes took place, firstly, the smaller grew relatively faster 

 and became as large as its neighbor, secondly, THE RELATIVE 



POSITION OF THE TWO GUTS HAS SHIFTED FROM ABOUT QO DEGREES 

 TO 130 DEGREES (Fig. 34). 



In the next specimen the two equal gastrulae are fused in such 

 a manner that their axes were about 140 degrees apart. Fig. 35 

 is a free-hand drawing of this pair. During the next two days 

 the gastrulae developed very slowly and unequally into a nearly 

 full-grown pluteus, and a gastrula just beginning to differentiate 

 its triradiate spicules. Their axes had in the meanwhile shifted 

 from about 140 degrees to 180 degrees (Fig. 36). 



The next example consists of a pair of somewhat unequal 



