SEXUAL CHARACTERS—ELASMOBRANCH FISHES 253 
yet succeeded in obtaining any specimens of Lernaeopoda scylli- 
cola, a copepod parasite, from within the siphon cavities, al- 
though that parasite is present almost without exception upon 
all the males, but not females, of 8. canicula that are obtained, 
both in the extracloacal aperture (the usual place of attach- 
ment), behind the pelvic fins, and even on the claspers them- 
selves, preferably upon the groove formed by their overlapping 
edges, and occasionally on the tips. Why their minute meta- 
nauplius larva is not occasionally sucked into the siphons is not 
yet clear, since it does not appear that the aperture leading into 
them is too small to admit of such a small organism. I think 
there is every possibility of such a discovery being made in the 
future. 
As has already been mentioned, the siphons make their appear- 
ance very early in development. Figure 3 represents a trans- 
verse section through the abdominal region of a young Scyllium 
canicula the day after hatching. At this stage the claspers are 
already visible and may be distinguished with a lens; the section 
reveals the presence of the siphons. 
In a young dogfish six days after hatching, the claspers are 
visible with the unaided eye and in length are about a quarter 
that of the pelvic fins. 
For the benefit of those who may desire to repeat the experi- 
ments upon the siphons, figure 4 represents a spermatozoon of 
the dogfish, with that of the skate introduced for comparison. ° 
It consists of a head or nucleus (v), an apical body which is 
cytoplasmic (a), a cytoplasmic middle piece (m), around which 
is wound a spiral of chromatin, granular or rhabditiform in 
appearance, terminating in tail or flagellum (f), which is ribbon- 
like save for a filamentous end-piece (e). The tail (e.f.) is from 
three to three and a half times as long as the anterior portion 
(a.n.m.). The head and apical body are best seen in a film 
preparation stained with haemalum and eosin; the spiral is 
thrown into relief in a similar preparation stained with night- 
blue and allowed to dry; the tail and end-piece are best dis- 
cerned in a similar preparation stained with night-blue and 
mounted in Canada balsam. 
