THE BURROWING BARNACLES (CIRRIPEDIA: ACROTHORACICA) 15 



Evidence alljdng this organ to the sexual process is indicated by the 

 fact that this perforation is not established until full maturity is 

 reached. If it were a vital necessity, one would think that it would be 

 established earlier in development. 



It was considered that this flap was associated with the barnacle's 

 lateral orientation, and the presence of large numbers of males under 

 the female. The males line the region of the burrow close to the proxi- 

 mal end of the flap. This would explain the necessity of eventually 

 establishing the opening at the distal end of the flap to provide a flow 

 of fresh water for the males, yet this opening is not required until after 

 the developmental period of the young female. A current of water is 

 maintained through this slit by movements of the mantle within the 

 burrow; this action can be seen readily in living material. 



The function of this external mantle flap, a structure unique in 

 Trypetesa lateralis females, has been a subject for investigation since 

 the discovery of the species. 



Methods: Many barnacles were collected and measured in the living 

 state (686 Specimens, 250 exceeding 0.3 mm aperture length). A record 

 was made of the length of the apertural slit of the female barnacle in 

 the shell, the number of barnacles in the shell, and whether an external 

 mantle flap had penetrated to the outer surface of the shell under 

 the barnacle. The shells containing these barnacles were then de- 

 calcified in a sufficient quantity of Bouin's fluid to weaken the shell 

 but not to free the barnacle completely. Then the shells were washed 

 with water and again evaluated for length of the slit and presence of 

 the external mantle flap penetration. 



The female barnacles were removed carefully and the males attached 

 to the females or to the burrow walls were counted. Frequently the 

 penetration of the flap could best be determined after the female 

 had been removed from the shell. 



Inasmuch as the flap would open frequently among bryozoan 

 colonies or serpulid worm cases, the presence of an opening could 

 not always be positively established. Uncertain specimens were not 

 considered in the data. 



Results: The results are shown graphically in figure 36c. The 

 numbers of specimens and the relative percentages are given. It can 

 be seen that most of the females whose external mantle flap do not 

 penetrate have no males, and those whose flap penetrates have males. 



A few females who have a penetrating flap and do not have a male 

 would be expected, even if a penetrance were required for males to 

 be present, inasmuch as the males may not settle on the female as soon 

 as space is available. The few specimens (four) with males and without 

 a penetrating flap seem unexplainable, but could be temporary or 

 misguided individuals, inasmuch as two of those four males were 



