THE GROWTH OF GROUPS 147 



fish were caught in considerable depths of the sea (200 

 to 400 fathoms) from a bottom of green mud. 



Nothing is to be gained by discussing the past history 

 of this group, since we know nothing about it. The 

 single specimen obtained by the Valdivia from near the 

 east coast of Africa is evidently of the narrow disorderly 

 type, judging from the careful description of it. It is 

 therefore certain that this particular type has been 

 established for a long time, and it may be the primary 

 type ; but since only one was obtained we cannot form 

 an opinion on this point, for the species may have been 

 polymorphic in that part of the world also. 



The narrow disorderly type was described as the type 

 of the species under the name M. lutea. Of the ten speci- 

 mens caught on the first occasion, from which the genus 

 was defined, five have passed out of the Indian Museum 

 in exchange : it is likely that some of them were of the 

 narrow disorderly type, so that this type may have been 

 the predominant one, on the first occasion of capture, 

 they are certainly larger in size than those of the other 

 type. At any rate, this type was in some way conspicuous 

 since it was regarded as the type of the species. The 

 characteristic of disorder was first only to be seen among 

 small individuals, hence it was regarded as a sign of 

 immaturity. Later on, however, when others of the 

 species were obtained it became evident that this was not 

 the case, for the character was seen to be present in some 

 fullgrown individuals. Hence there is no doubt that 

 the species is polymorphic, the several forms being re- 

 cognizable. Although the facts of the case cannot be 

 tested experimentally, yet there is reason to believe that 

 the attributes of order and disorder in the arrangement 



