smallwood: maturation of haminea solitaria. 299 



must involve a complete structural rearrangement of their material. If 

 there is to be a subsequent qualitative reduction, some kind of a sym- 

 metrical arrangement of this material is necessary in order that there 

 may be subsequently an equal division ; but the forming chromosome 

 usually becomes irregular in outline, rendering improbable a symmetri- 

 cal arrangement of its constituent elements. 



So far as I know, the existence of two processes or methods in matura- 

 tion has never been observed in other animals, except that Lillie (:0l) 

 found in one instance that in Unio the egg exhibited two quite distinct 

 processes in the formation of the second mitotic figure. In explanation 

 of this phenomenon he says (pp. 243, 244) : "The modification was 

 undoubtedly due to some slight ditference in the conditions of the cyto- 

 plasm in the two cases. That such different courses of events can yet 

 lead to the same typical results indicates a most remarkable power of 

 self-regulation of the entire ovum, and at the same time demonstrates 

 that the mechanical processes of spindle and aster formation are not the 

 primary factors in determining the position of the maturation spindles," 

 The striking fact in Haminea is that the direct process recurs in nearly 

 as many eggs as the indirect, both accomplishing the same result, — the 

 formation of the second polar cell. 



3. Fertilization. 



In Haminea, after copulation takes place, the hermaphroditic duct is 

 full of spermatozoa, which are most abundant in the lower and larger 

 part of the duct, but may be found even in its branches. 



The eggs and spermatozoa of the same individual are often found 

 together in the follicles of its hermaphroditic glands. That these sper- 

 matozoa are mature, or nearly so, is to be inferred from the fact that 

 they are all discharged during copulation, sections of such an ovotestis 

 made after copulation showing only quite immature spermatozoa in these 

 follicles. Nevertlieless, self-fertilization does not take place, so far as I 

 have been able to determine, since no sperm heads are found in the egg 

 between the time when copulation takes place and the time when the 

 egg passes into the hermaphroditic duct. 



My studies on the spermatozoon have not been at all exhaustive. The 

 mature spermatozoon (Plate 9, Fig. 60) is composed of the two parts, 

 head and tail. The head is cylindrical, flattened, and of nearly uniform 

 thickness, terminating rather bluntly at each end ; it is distinctly bent 

 near the middle. The portion anterior to the bend is somewhat shorter 

 and more pointed than the part behind the bend. The tail is long and 



