INHERITANCE 725 



Even within a single clone there is variation in characters, though much 

 less than when different clones are taken into consideration. Different 

 individuals of the same clone may differ greatly in number and length 

 of spines, slightly in size of the body, very slightly in the number of 

 teeth. 



In vegetative reproduction, the offspring resemble the parent, but 

 not completely. The general rule is that parent and offspring are alike 

 in respect to characters that distinguish different biotypes or races, but 

 they need not be alike with respect to characters in which different indi- 

 viduals of a clone are diverse. The type of inheritance will be seen from 

 examples of the numbers of spines in successive generations in certain 

 clones ; 



Clone 1 

 Clone 2 

 Clone 3 

 Clone 4 



2—2—5—4—6 

 1—2—1 — 4 — 2 — 3 

 6—6—6—6—4—5—7—6 

 0—0 — — — 1 — — — 1-0 



Thus clones differ from each other in the fact that some usually have 

 few spines or none, others a slightly larger number, others a still larger 

 number — though within each clone there is variation. A given biotype, 

 or clone, is characterized by a certain average number of spines; another 

 by a different average number. In respect to the average numbers of 

 spines, many different biotypes may be distinguished. 



When from a single clone individuals differing in number of spines 

 are allowed to multiply until each has produced many descendants, the 

 usual result is that the average number of spines in the two sets of 

 descendants is the same. Thus in clone 1 above, the individual with 2 

 spines and that with 6 spines would, as a rule, produce descendants 

 having the same average number of spines. The individual differences 

 within the clone are usually not inherited; the mean differences between 

 biotypes are inherited. 



To what are due the differences in numbers of spines or in other char- 

 acteristics, between the different members of the same clone, illustrated 

 above? The shell is produced complete at the time that reproduction 

 occurs. The individual about to reproduce buries itself in a mass of 

 soft debris. The protoplasm swells, projects from the mouth of the 



