410 BOWEH. 



inner surface. In Figure 15 this irregularity can be clearly seen (in 

 optical section), and this uneA"enness is reflected in the surface views 

 in which the chromatic layer is ver}^ unevenly stained, giving the im- 

 pression of ^■acuoles (Fig. 15). Of rather regular occurrence at this 

 time is the appearance at one side of the head and about midway of 

 its long axis of a clump of chromatic material (Fig. 15), which will be 

 again referred to presently. The most striking feature, perhaps, is the 

 absence of any groove formation along the head, so characteristic of 

 the normal sperm heads (see Bowen '22fl). This groove does not 

 appear ever to be formed at any subsequent stage, — at least in a 

 fairly representative series of cross-sections I have failed to find it at 

 all. ^ 



The pseudoblepharoplast noAv disappears (Fig. 16) as in the normal 

 cases, but from this point on the course of events is otherwise strik- 

 ingly different. The chromatic layer becomes very highly 'vacuo- 

 lated' (Fig. 16), and a tendency is noticed toward the formation of 

 what appear to be two large vacuoles, one located in front of, the 

 other behind the mid-axial clump of chromatic material which was 

 forming in Figure 15. The chromatic layer is prett}^ well broken up, 

 though a definite zone seems to be retained along one side of the head 

 as shown on the anterior vacuole in Figure 16. This stage is a very 

 characteristic one in Mvrganiia, and is particularly striking because 

 of the bizarre appearance gi^-en by the chromatic arrangements. 

 Apparently this condition is of very short duration, for the two clear 

 areas soon fade out and the whole head appears stained in an indefi- 

 nitely irregular way except for a clear area at the base corresponding 

 to the same characteristic of the normal sperm. The head elongates 

 very rapidly especially during the latter part of this stage, and it is 

 during this period that the great difference in length between the large 

 and small sperm heads is established. The arrangement of the 

 chromatic material is simply the same indefinite, vacuolated condition 

 characteristic of the earlier stages (Fig. 17). \Yhether the chromatin 

 remains peripheral or becomes distributed through the cavity of the 

 head is not known. This peculiar arrangement of the chromatin per- 

 sists into the next stage and is probably directly comparable to the 

 vacuolation of the chromatin which I have described in the normal 

 sperm heads of Murgantia (Bowen '22a). 



Stage o. The condensation of the chromatic material to form the 

 definitive sperm head. — In stage o the chromatic material undergoes 

 a process of condensation the result of which is to produce a sperm 

 head in structure essentially like that of the normal sperms. As in 



