TUBIFEX. 385 



Both Vejdovsky and Lankester state that not all the tail 

 is embedded in the cementing material, bnt that a small 

 portion lies outside, so that the whole spermatophore is 

 surrounded by the free ends of the spermatozoa. The 

 spermatophores which I have examined show a certain 

 amount of variation in this respect. In many cases the 

 tails are undoubtedly partly free from the cementing 

 material, and the free ends are placed at right angles to 

 the longitudinal axis of the spermatophore, and not 

 obliquely to it. In some cases, however, the layer of 

 cementing material is thicker than in others, and when 

 that is so there is no portion of the spermatozoon lying 

 free. Whether this is an abnormal condition, or merely 

 due to the amount of cementing material present, is very 

 difficult to decide. 



Lankester' s description differs from this in several 

 details. He states that there is a narrow, highly 

 refringent band outside the axial cylinder and another 

 of similar nature outside the layer of cementing material 

 and spermatozoa, between it and the free ends of the 

 tails of the spermatozoa, the latter being in constant 

 vibratile motion. He also says that the whole spermato- 

 phore exhibits movement when liberated from the 

 spermatheca into a dilute salt solution. Although I have 

 performed this operation many times, I have never 

 succeeded in persuading the spermatophore to exhibit the 

 active movements which have been described. Further, 

 Lankester believes that the head of the spermatozoon is 

 much elongated, of almost the same length as the tail, and 

 that the head as well as part of the tail is buried in the 

 cementing material towards the outside of the spermato- 

 phore. I think there is no doubt that the heads of the 

 spermatozoa lie just outside the axial cylinder, but very 

 close to it, and are confined to the deeply staining zone 



