CHAKl.KS B. MKTZ 27 



resembles the figures of I^illie (47) for fixed and sectioned sperm in contact with 

 the egg. 



Information concerning the mechanism of acrosome filament formation 

 might result from electron microscope examination of sectioned spermatozoa. 

 Afzelius (i) has examined sectioned sperm of four species of sea urchins. In 

 all of these the acrosome contains a terminal granule of osmiophilic material 

 and a less osmiophilic basal 'cavity' projecting into the sperm nucleus. In one 

 of the four species, namely Echinocardiiim cordalum, the terminal granule is 

 located at the end of a stalk and this stalk ai)pears to be tilled with the same 

 material as the basal cavity. However, in some preparations the stalk material 

 appears to be oriented as longitudinal libers or broken into flakes. Echino- 

 cardium is the only species that has been examined both for acrosome fila- 

 ments and in sections. Comparison of the figures of Afzelius (i) and Rothschild 

 and Tyler (94) indicates that Afzelius examined sperm that lack acrosome 

 filaments. This is of further interest, for Afzelius prepared his material by 

 dropping undiluted semen into his fixative. The fact that sperm prepared in 

 this direct way lack filaments supports the view that the compact condition 

 of the acrosome is the initial one. 



Afzelius suggests that the acrosome particle of sea urchin sperm contributes 

 to the dispersing material described by Dan (22) in discharged acrosomes and 

 that the less opaque, often fibrillar material corresponds to the central core 

 of the filaments. This may prove to be the case in certain instances, but as 

 yet no substantial evidence is available to support this view. Furthermore, the 

 Echinocardium filament figured by Rothschild and Tyler (94) is a very long, 

 finely tapering structure and shows no appreciable dispersed material. Dan's 

 suggestion that acrosome filaments may be discharged in trichocyst-like fashion 

 at least has the merit that in both acrosomes and trichocysts there does not 

 appear to be a highly organized, preformed structure in the undischarged 

 organelle. 



Aside from inducing acrosome filaments, treatment of sperm with egg water 

 appears to have a second morphological effect, namely a loosening (23) or 

 displacement of the sperm mid-piece (83, 94, 117). The significance of the 

 mid-piece effect is not apparent. ^Moreover, the mechanism of this effect would 

 seem to be complicated, for electron photomicrographs show that this structure 

 is a single, continuous ring with a central canal for passage of the sperm tail (i) 



These studies are clearly in an early stage of development. More organisms 

 may need to be examined, more quantitative data obtained and a thorough 

 series of specificity studies carried out with respect to the action of egg water. 

 Finally, the active agent in egg water requires characterization. Its identifi- 

 cation with or separation from the specific sperm isoagglutinin, fertilizin, is a 

 problem of special interest. However, the data now available suggest the in- 

 teresting possibility that the spermatozoan is subject to a trigger reaction 



