Preliminary Notes on Growth-Stages in 
Brittle-Stars 
Arthur 8S. Campbell 
There are a number of conditions to account for our present 
lack of a rational system of the brittle-stars. One of the principal 
reasons why the group is so difficult to classify lies in the profound 
ignorance of their growth-changes. The excellent systematic 
work of Ljungman, Lutkin, Lyman, Koehler and the two Clarks 
have brought some thousand species to attention but the real rela- 
tionship of these as larger groups is yet quite unsolved. There have 
been several attempts to rationalize the classification, one by Bell, 
1892, and more recently by Matsumoto, 1915. Neither of these sys- 
tems is thoroughly based upon phylogenetic history, and hence, can- 
not be conclusive since the state of our present knowledge is such 
as to forbid any sweeping generalizations. 
Although the chief reason for our lack of a rational system in 
the group is this lack of attention upon growth-stages, another 
lies in the general disregard of palaeontological evidence, and a fur- 
ther reason because attention has been focused upon larval, rather 
than post-larval, stages. 
Material heretofore studied in connection with this problem 
of growth-stages in the young of ophiurans numbers less than one 
dozen species, all of which are Atlantic or West Indian forms. My 
own observations were made upon seven species, the members of 
five families. All are the members of the littoral fauna of Southern 
California. Specimens were collected in all accessible habitats and 
studied after preservation. 
The excellent plates for this paper are the work of Miss E. 
Keyes, a student in Pomona College. 
It is not always possible to tell just why one places a form in 
this or that group for many characters are subtile and one is obliged 
to depend very often upon general features. Especially is one 
dependent upon as complete a series as possible in placing a juve- 
nile. H.L. Clark, in his paper on growth-changes in some brittle- 
stars expresses the only formulation of the very important con- 
tribution of R. T. Jackson to the study of juvenile brittle-stars that 
I have seen. This law is a very real help in determining possible 
relationships between specimens otherwise obscure or impossible 
to differentiate. Briefly stated, we may say that, as applied to 
these forms, the base of an arm of a young form corresponds ex- 
ceedingly suggestively with the tip of an arm of an adult specimen 
of the same species. However, the extent of localization varies 
greatly in different species, as I have found. One needs much 
study to determine accurately the position of a given specimen. 
