236 O. C. GLASER. 



paper read before the Research Seminar at Wood's Hole in the 

 summer of 1905. This view may still appeal to some as valid, 

 but I think that certain facts then unknown to me point strongly 

 in the opposite direction. While it is true that during the early 

 stages of cannibalism the increase in the size of the embryos is 

 mere stretching due to the ingestion of eggs, such stretching is 

 not all that happens in the larvae. It will be recalled that the 

 entoderm in stage I. is a pretty thick layer in which cell boun- 

 daries are obscure. An examination of the layer however will 

 show that if cell boundaries were distinct, the cells would be 

 cuboidal, or rectangular or at most diamond-shaped (see Fig. 2). 

 After the larvae have taken on the form of stage III. the entoderm, 

 as Fig. 3 shows, has an entirely different appearance, and the 

 distinct outlines of the cells show that these instead of having the 

 shape of cubes or rectangles, or diamonds, are spindle-shaped, 

 and provided with long processes that by fusion with corres- 

 ponding elongations from neighboring cells form a continuous 

 membrane. I think that no special argument is necessary to 

 support the view that the transformation undergone by the ento- 

 derm cells when the larvae pass from stage I. to stage III., is the 

 direct result of stretching. Such an effect is to be expected. 

 This condition however is not final. The elongated entoderm 

 cells soon lose the characteristics which they exhibit in stage 

 III. and return to a condition more nearly like that in stage I., 

 except for two general differences : boundaries are more distinct 

 than in the younger entoderm, and regional differentiation is 

 observable. 



These metamorphoses are of great importance. If the larvae 

 decreased markedly in size during the later stages of their develop- 

 ment, and as the result of such shrinkage approached the size of 

 the pre-cannibals, the conversion of the spindle-shaped cells of 

 stage III. into the cuboidal cells of stages IV. and V. could be 

 attributed to this cause : to decreased stretching. The idea that 

 the later stages in development might be smaller than the earlier, 

 is somewhat bizarre when viewed in the light of our knowledge 

 of ontogeny in general, for the exact reverse is law. Neverthe- 

 less such decrease in Fasciolaria embryos is quite easily conceiv- 

 able as the size depends on what the larvae contain. If metab- 



