26 UNITED STATES NATIONAL MUSEUM BULLETIN 296 



Kefer to the diagram (fig. 45) for a partial reconstruction of the 

 spermatozoan tail region. The electron microscopist was Fred D. 

 Warner, who also reconstructed the figure of sperm anatomy. The 

 magnification is 20,800 X . 



The Lack of a Penis in Trypetesa lateralis 



Introduction: The purpose of this project is to clarify whether or 

 not the male of T. lateralis has a penis. Hundreds of males had been 

 cursorily examined in the course of sixteen years of study on this 

 species, without a penis being seen. A specific study for this purpose 

 was undertaken by Richard Taverna, one of my assistants. 



Methods and materials: T. lateralis specimens were collected 

 in Tegula shells occupied by hermit crabs at Moss Beach, San Mateo 

 County, CaUfornia, during October and November 1966, and in the 

 spring of 1967. After the barnacles were found, they were placed, 

 while remaining in the shell, in sea water in a 4-inch finger bowl at 

 20° C. Ascorbic acid was added to the sea water to some specimens 

 (0.5 g/150 ml) for different lengths of time. Such stimulation has been 

 demonstrated to stimulate sexual activity in the Thoracica (Collier, 

 Ray, and Wilson, 1956). 



Removal of the barnacle was accomplished by decalcification of the 

 shell in 10-percent HCL and 10-percent formalin. Final removal of 

 the barnacle was accompHshed with the use of fine forceps. The male 

 and female then were placed in glycerin as a means of partial clearing. 

 After penetration of the glycerin, the male was removed from the 

 female with ultra-fine forceps and placed on a slide. The male was 

 mounted in glycerine with a raised cover-slip to prevent distortion. 



Results and observations: The observation of 121 isolated 

 males was not successful in finding a trace of a penis. 



The male barnacle of T. lateralis did not show any signs of penis 

 formation, either in the ascorbic acid or in ordinary sea water. The 

 failure in either case not to form a penis suggests that either no 

 penis is formed by this organism or that other environmental factors 

 not present at this time of year have yet to be explored. 



Conclusion: According to the present findings, there is no evi- 

 dence for the existence of a penis or other sex organ in T. lateralis. 



Activation of Acrothoracican Sperm 



The sperm of Trypetesa lateralis can be activated by rupturing 

 mature males in sea water. The length of time it takes for the sperm 



