THE RELATIONSHIPS OF THE SEA-SPIDERS. I49 



larval appendages change into those of the adult — the 

 palps and ovigerous legs. 



We may now take up another type of development 

 found in the group, and represented by the genus 

 Pallene, which, I may say in passing, is to be regarded 

 as a much modified and abbreviated development of a 

 form like the last — Tanystylum. 



The egg has one hundred and twenty-five times the 

 volume of the preceding species. Corresponding with 

 the increase in the size of the egg is a decrease in the 

 number, and correlated with the addition of food-yolk to 

 the egg is the abbreviated development ; so that the 

 young leaves the parent — not in an immature state as 

 in Tanystylum — having almost all of the structures of 

 the adult. 



The segmentation of the egg is holoblastic as in the 

 last case, but the first cleavao:e furrow divides the e^s: 

 into a small cell — the micromere — and a larger one. 

 The protoplasm surrounding the nucleus is free from 

 yolk in all cases ; but from this purer protoplasm, pro- 

 cesses ramify all through the yolk. It is needless to 

 follow, for our purposes, the egg through the series of 

 segmentation phases which follow, and it will be suffi- 

 cient for us to know that the result of these changfes is 

 a solid mass of cells much as in the case of Tanystylum. 

 There is this difference, however, that in Pallene the 

 cells covering one pole of the egg — those which have 

 come from the micromere — are smaller than those over 

 the rest (two-thirds) of the egg. It is in the region of 

 these smaller cells that the first indications of the 

 embryo appear. 



After the segmentation is completed follows, as in the 



