A. A. MERLIN OX THE SPERMATOZOON OF THE RAT. 193 



2. Further, towards the posterior end of the " head " a band 

 of deeply stained endopkism branches off and passes diagonally 

 across to the convex edge, along which it extends for a consider- 

 able distance, as figured. The whole of this portion of the 

 endoplasm is not usually as distinctly definable or so Avell 

 marked as that previously described. 



3. Still nearer the posterior end a broad diagonal band 

 stretches from the concave to the convex edge, in parts of 

 which indications of differentiated structure have been stroncrlv 

 suspected. 



4. A deeply stained, triangular-shaped mass of endoplasm 

 where the middle-piece joins the head. 



5. Two external notches on the under concave edge, that 

 nearest the tip being less frequently well marked than the other. 



Fisr. 2. 



Figure 2 represents the appearance of a portion of the tail 

 with a considerable length of core exposed. This core has been 

 subjected to a most careful and critical examination, and has 

 been found to exhibit indications of a longitudinal striation, as if 

 built up of many extremely minute fibres. It slightly bulges 

 half way along its exposed length, as though freed from the 

 constricting influence of its sheath. The tail and middle-piece 

 appear mottled ; but this effect may Ido due to the core seen 

 through the sheath. I have endeavoured to faithfully represent 

 the appearance in the figure. The spiral fibre running round 

 the middle-piece has not been seen, possibly owing to the method 

 of preparation not being favourable to the demonstration of this 

 feature. 



When observing this organism under the best conditions, with 

 a fine aprochromatic objective of N.A. 1*426 and a large solid 



