326 EDWIN E. REINK!.. 



rounded the centrosome remain at the posterior end of the sper- 

 matozoon. 



The species of Littoritia in which have been found a free nurse- 

 cell to which the spermatozoa are attached are L. an^ulifera, L. 

 nebulosa and L. rndis. The first two species were studied at 

 Port Royal, Jamaica, along with Strombus bitnbcrcnlatits, and 

 they too were identified by Dr. Pilsbry. 



If the sperm-ducts of L. nebulosa or L. rudis are ruptured, 

 the contents, when diluted with sea-water, will appear under the 

 microscope as a great number of spheres to each of which is 

 attached a tuft of spermatozoa. The spheres are nurse-cells 

 composed of vacuolated yolk bodies and a degenerate nucleus 

 (Fig. 5). The nurse-cells of L. angulifera differ from those of 

 the other two species in that here the yolk bodies arc not vacuo- 

 lated and they partly enclose a long thick cytoplasmic rod to 

 one end of which are attached the spermatozoa. In all three 

 species only the perforatoria and possibly the tips of the heads 

 of the spermatozoa are inserted into the cell. 



The first movement to be seen is a rhythmical and uniform 

 beating of the tuft of spermatozoa which sends the nurse-cell 

 rapidly forward. Later the spermatozoa beat independently and 

 the tuft spreads. Very frequently the spermatozoa of one nurse- 

 cell become entangled with those of another; in that event the 

 nurse-cells are drawn together and held by an agglutinous sub- 

 stance forming the pabulum in the cell into which the spermatozoa 

 are inserted. In this way a great many nurse-cells are drawn to- 

 gether and from such a mass the spermatozoa may later be seen 

 protruding on all sides and beating iv.nularly like cilia. This 

 beating of the spermatozoa will continue for several hours. 



In case a nurse-cell has not become entangled with others, the 

 spermatozoa soon free themselves; their heads become further 

 and further separated from the nurse-cell until the attachment 

 is completely lost. A sperm thus freed is seen to h.i\c a long, 

 thin perforatorium behind which is the head; tin- latter passes 

 almost imperceptibly into a very long tail (Fig. 3). After tin- 

 spermatozoon has been swimming about in the wau-r for a time 

 the perforatorium becomes swollen; this is what has usually been 

 figured as the sperm head. The whole process can be seen to 

 better advantage in Fasciolaria. 



