660 D. B. CASTEEL 



(fig. 31). The nucleus retains contact with the original outer 

 surface of the outer tube and is carried to the opposite end of 

 the spermatozoon, where it now lies within the tube. The rem- 

 nant of the finger-form process and the gelatinous envelop of 

 the original outer tube are also carried within the tube as it slips 

 backwards and turns inside out. Within the nuclear end of 

 the completed tube, as represented in figure 31, is a long, some- 

 what coiled, flagellum-like structure (/) which extends downward 

 in the tube from the mass of protoplasm which surrounds the 

 nucleus. 



The final steps in metamorphosis occur just before the sperma- 

 tozoon leaves the spermatophore sac and immediately there- 

 after as it lies within the oviduct. At this time the flagellum 

 pushes past the nucleus and outward through the open end of 

 the tube (fig. 32) and soon is completely protruded (fig. 33). 

 The nucleus also slips out of the tube and lies imbedded in the 

 base of the flagellum. The opposite or mitochondria-bearing 

 end of the sperm tube now changes somewhat in form. It 

 becomes flattened and ridged as shown in figure 34 and a circlet 

 of short processes appears around the vesicle which crowns the 

 tip-end of the tube. 



The extremely bizarre form of the spermatozoon of the tick 

 makes difficult the task of homologizing its parts with those of 

 other spermatozoa. In the case of Argas about the only land- 

 mark which one can use is the nucleus, for no centrosomes are 

 visible at any stage of spermatogenesis, and the highly complex 

 processes of metamorphosis obliterate or mask the characteristic 

 features of typical spermatozoa. Using the final position of the 

 nucleus as a guide, one is led to the conclusion that the morpho- 

 logical head of the spermatozoon is that end of the completed 

 tube in which the nucleus lies. One would naturally expect that 

 this would be the forward end of the moving spermatozoon 

 but such is not the case. The living spermatozoon of Argas 

 does not exhibit locomotion until it is completing its develop- 

 ment in the spermatophore sac in the oviduct of the female, 

 at which time it moves with the mitochondria-bearing end in 

 advance. This observation is in harmony with the conclusions 



