2O4 C. M. CHILD. 



which the nuclear membrane is still intact. I am forced there- 

 fore to the conclusion that only a part of the nucleus is concerned 

 in the formation of the sperm-head, the remainder undergoing 

 degeneration. Fig. 49 (PI. XV.) represents a cytophore after con- 

 densation. For the sake of clearness only a few of the nuclei 

 which cover the surface of the mass are represented as they 

 appear, the others being indicated by dotted lines. In several 

 cases what seems to be the sperm-head is visible in the degen- 

 erating nucleus. 



Fig. 50 (PI. XV.) represents a case in which the spermatozoa 

 are apparently just separating from the cytoplasm of the cyto- 

 phore which contains the deeply staining remains of the nuclei. 

 In this case I convinced myself that these were the anterior 

 ends of the spermatozoa, by following the tails throughout their 

 whole length in the testis. The diameter of the ends shown in 

 the figure was distinctly though only slightly greater than that 

 of the other ends, but the change in diameter is very gradual. 



In the free spermatozoa no differentation in staining of the 

 head-region is visible. The whole spermatozoon stains uniformly 

 and less intensely than the nuclear granules or masses of earlier 

 stages. In a few cases I believed I had distinguished slight traces 

 of the two nuclear granules in the fully developed spermatozoon 

 but these observations were so doubtful that no figures are given. 



In the fresh spermatozoa obtained by teasing in indifferent 

 fluids no visible head and no movement was ever observed. An 

 examination of the bibliography of the subject afforded scanty 

 results. So far as I have been able to determine no full account 

 of the spermatogenesis of the cestodes exists. Among the older 

 papers several give brief descriptions of the formation of the 

 spermatozoa but these are either very incomplete or incorrect in 

 consequence of the technique employed and need not be reviewed 

 in detail. In one point, however, the early observations agree 

 fairly well : the head of the spermatozoon is described and fig- 

 ured as exceedingly minute or is said to be absent. Sommer 

 and Landois l in describing the testes of Bot/iriocepkahis latus 

 mention spermatozoa bearing at one end " ein kleines, stark 

 lichtbrechendes Kopfchen." 



1 Sommer and Landois, " Ueber den Bau der geschlechtsreifen Glieder von Both- 

 riocephalus latus Bremser," Zeitschr.f. wiss. Zoo!., Bd. XXII., 1872. 



