BRIEFER ARTICLES. 
A CASE OF VARIATION IN THE NUMBER OF AMBU- 
LACRAL SYSTEMS OF ARBACIA PUNCTULATA. 
HENRY L. OSBORN. 
THE growing interest in variation, stimulated by the appearance of 
Bateson’s' work on that subject, seems to make it worth while to 
record cases of variation even where they are isolated, and it is for 
this reason that I make the following record. The specimen is the 
only one thus far met with in the course of several years in using 
Arbacia and Strongylocentrotus, so that it can be regarded as rare. 
The number of Arbacias that have passed through my hands cannot 
be less than two hundred, and of Strongylocentrotus, not less than 
twice that number, and I have not before met a case in which the 
number of ambulacral systems was less or more than five. I was, 
therefore, somewhat surprised when a student presented me with a 
drawing of an Arbacia in which the number was four, and at first 
was inclined to doubt the accuracy of the work; but the specimen 
itself was placed in my hands and showed that this departure from 
the typical number does occur in this species. 
The specimen came to me dried. It came from Woods Holl in a 
lot of supplies furnished by Mr. W. H. Walmsley, and the position 
Aboral and ] oe IRET > E ERA E ie, ge gee 
from the coast of Massachusetts. 
of the soft parts can only be inferred from the test, which, however, 
is fairly indicative of the internal anatomy in this class of animals. 
Two views of the test are shown in the accompanying cut. That of 
1 Materials for the Study of Variation. Macmillan, 1894. 
