294 NATHAN FASTEN. 



hollow distal end of the central body which is also extruded, exerts 

 a pull on its solid proximal portion, transforming it into a spine- 

 like structure (Figs. 72-76, 6), which stains intensely black with 

 Heidenhain's haematoxylin. While these changes are going on, 

 the nuclear-mitochondrial cup loses its rays and rounds out into a 

 spherical body. 



When the second vesicle has been completely extruded (Fig. 

 75, z/), then the first vesicle (Fig. 75, v) commences to evert and 

 continues this process until it is completely turned inside out. 

 These steps may be observed in Figs. 75-79, v. During the 

 eversion, the darkly staining proximal end of the central body 

 forces upward on its tubular distal portion until the latter is 

 finally extruded completely to the outside (see Figs. 75-77, 6). 



The completely exploded spermatozoa present the appearances 

 represented in Figs. 78 and 79. The upper portion consists of 

 the second vesicle (v'), in the interior of which is contained the 

 everted first vesicle (v), with its upwardly projecting spine-like 

 body (&). The lower portion consists of the nucleo-mitochon- 

 drial cup (A), which has transformed into a more or less spherical 

 structure. In many cases, stages like those shown in Fig. 80 

 were seen. These evidently are exploded spermatozoa in which 

 the second vesicle has completely ruptured and disintegrated. 

 Binford ('13) has observed similar conditions in Menippe mer- 



cenaria. 



6. DISCUSSION. 



A. Sy nap sis. 



During the last few years the parasynaptic view of chromo- 

 somal conjugation has been established in numerous species of 

 animals. In 1900, Von Winniwarter first advocated parasynap- 

 sis amongst the mammals, but the view did not become firmly 

 established until the Schreiners ('04, '05, '06, '07 and '08) pub- 

 lished their important researches on the germ cells of many ani- 

 mals including mammals, birds, reptiles, amphibians, fish, 

 molluscs and annelids. Of late the parsaynapsis view of Von 

 Winniwarter and the Schreiners has been extended to a great 

 many additional forms, and excellent reviews of the vast litera- 

 ture on this subject may be found in the recent publications of 

 Montgomery ('u), Wilson ('12), Fasten ('14) and Wenrich ('16). 



