332 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



But I have been unable to determine whether this disappearance is the 

 result of disintegration, or whether the cell membrane unites with the 

 nucleus. The spermatozoon now appears to be mature, and by teasing 

 out fresh tissue is seen to swim actively by means of the tail. 



For the sake of comparison with the spermatozoon of other coelen- 

 terates it may be well to describe its structure in the finished condition, 

 which is shown in Figure 102. The head measures 2.5 p in length, the 

 middle piece 1 fi, aud the tail at least 15 /x, but I have not been able to 

 determine the extreme length of the latter. Tiie head and middle piece 

 together have a broadly conical outline when seen from the side, but are 

 circular in polar view. The nucleus is conical with a nearly flat base 

 and slightly truncate tip ; as a whole it stains homogeneously and deeply, 

 exhibiting no distinct chromatic structures, except a dense, more deeply 

 staining plate at its base (Fig. 102), which is, perhaps, derived from the 

 basal chromatin mass of the stage shown in Figure 96. Closely in con- 

 tact with the truncate apex of the nucleus is the acrosome, a spherical 

 or oval body which exhibits the characteristic archoplasmic staining 

 reaction. A well-marked middle piece can now be distinguished, the 

 axis of which is the axial filament connecting the distal centrosome with 

 the base of the nucleus, the sheath or mantle consisting of the archo- 

 plasmic bodies. Upon the disappearance of the cytoplasmic mantle, 

 these bodies are seen to be spherical masses of considerable size, usually 

 two in number. In many cases, however, I have clearly distinguished 

 three or even four, so that we have in Goniouemus a condition com- 

 parable to that described by Retzius (:05) in Tubularia, Clava, Sertu- 

 laria, Halecium, and certain actinians and lamellibranchs, where he finds 

 that the number of archoplasmic masses in the middle piece of the sper- 

 matozoon is variable. The only persisting trace of cytoplasm is a very 

 thin layer covering the base of the middle piece ; at the margin of this 

 the distal centrosome can be distinguished in favorable cases as a minute 

 dark granule. The portion of the axial filament between the two 

 centrosomes is usually entirely masked by the archoplasmic bodies, 

 though occasionally, especially in maceration preparations, it is visible ; 

 but the proximal centrosome can no longer be detected. The question 

 whether it still persists, or has actually disintegrated, can not be defi- 

 nitely answered. The tail consists of a single delicate fibre. It seems 

 to arise from the distal centrosome, through which it is directly contin- 

 uous with the axial filament of the middle piece ; this is an argument 

 for believing that the latter is a true fibre and not merely a modified 

 "track "in the cytoplasm or archoplasm, as has sometimes been sug- 



