338 CRESSWELL SHEARER, WALTER DE MORGAN, H. M. FUCHS. 
These characters are tliose developed in the early pluteus — in 
particular the larval skeleton. This is a structure w^hich 
varies very readily with the state of health of the organism, 
and the variations in one form frequently tend to give it a 
shape resembling that of another. For instance, the skeleton 
of the antero-lateral arms of the Echiims pluteus is a simple 
rod, but in abnormal cases a lattice form is developed like that 
of Sphserechin us. For this reason it is evident that the 
skeleton is an unsatisfactory index of heredity, and it would 
seem to be doubtful if much of the previous work on inherit- 
ance in the very early pluteus is of substantial value. 
In the forms which we have studied we have been forced 
to adopt larval characters later than those hitherto used as 
criteria of inheritance. This has been rendered possible by 
the elaboration of methods of rearing healthy larvae in 
quantity up to and beyond metamorphosis. In the advanced 
plutei of Echinus we have found chai’acters which do not 
vary in the parental forms and which are present in the one 
species and absent in the other. 
Our experiments have been made with the three common 
English species of Echinus, namely E. esculentus, E. 
acutus and E. miliar is. The characters, of which we have 
investigated the inheritance, have been as follows: E. 
esculentus and E. acutus both develop posterior as well 
as anterior ciliated epaulettes (PI. 17, figs. 2, 3) . E. miliar is, 
on the other hand, has no posterior epaulettes, but two pairs of 
green pigment-masses are formedin the anterior epaulettes (PI. 
17, fig. 1). All the hybrid plutei have in previous years been 
purely maternal with respect to these characters. Thus in 
the crosses E. esculentus S x E. miliaris c? (Tl. 17, fig. 5) 
and E. acutus ? x E.miliaris S (Ph 17,fig. 4) the posterior 
ciliated epaulettes are developed, although not to so great 
an extent as in E. esculentus or E. acutus, but the green 
pigment-masses are absent. In the crosses E. miliaris ? 
X E. esculentus c? (Ph 18, fig. 8), and E . m i 1 iaris ? x 
E. acutus c? (Ph 17, fig. 6), on the other hand, the posterior 
epaulettes are absent and the green pigment is present. 
