324 ME. P. H. GOSSE ON THE DHECIOUS CHAEACTEE OE THE EOTIFEEA. 
The mass is sometimes broken up into fragments of irregular size and shape, and some- 
times apparently pulverulent. In general, it appears to lie loosely in the midst of the 
granular amorphous matter that occupies the posterior region of the body-cavity ; but in 
Brack. Pala, and especially in B. amj^kiceros., I have fancied that I discerned traces of 
a vesicle, within which the white substance seems to be contained. 
41. On the nature of this substance I have no light from personal research. Dr. 
Leydig, however, considers it to be a urinary concretion (Harnconcremente), analogous 
to the chalky fluid which is discharged by many insects, immediately after their evolu- 
tion from pupa. 
42. In the male of Asplanchna Brigktwellii, there is, as its discoverer observes, “ a 
conspicuous round sperm-vessel, or testis, in which spermatozoa in active vibratile 
motion may be seen Mr. Dalrtmple, and subsequently myself, also saw these, both 
within the sac and discharged by pressure. Each spermatozoon, according to my own 
observation, consists of an oblong body, y /ao th of an inch long, and an abrupt, slender, 
vibratile tail, of equal length. In the sperm-sac of A. Sieholdii, Dr. Letdig flnds various 
seminal elements, viz. round cells ; pyriform cells, drawn out to a flne point, and 
adhering to each other by their rounded ends, in a stellate manner ; oblong bodies, with 
one side dilated into a free, undulating, membranous border ; and slender, stiff', rod-like 
bodies, with a central swelling; all containing nucleated nuclei f. On the male of 
A. priodonta., my observations were too limited to determine more than the existence 
of the globular sperm-sac. 
43. In Brachionus ruhens and B. Mulleri I found spermatozoa, which I have above 
described (§§ 13 and 26). In the latter, the sperm-bag is of great size, and contains, 
besides the spermatozoa of unusual development, slender spiculiform bodies (flg. 23), 
which may be the equivalents of the little rods described by Dr. Letdig in Aspl. Sieholdii. 
The sperm-bag (in Br. Mulleri) is closed posteriorly, as it is also in Aspl. Brighfwellii, 
by what appears to be a true sphincter (flg. 20 ) ; and such I conjectui'e to be the expla- 
nation of those diverging lines which M. Dujardin saw in Entey'oplea (so-caUed), which 
he considered to be pedicels of his “ touffes de granules,'" while the “ touffes ” themselves 
I take to have been the masses of urinary concrement. Dr. Leydig, however, considers 
the whole to have been masses of spermatozoids. 
44. The outlet of the sperm-bag is, in all cases, by a thick protrusile and retractile 
penis. Wherever a foot exists, this intromittent organ is continuously miited to its 
dorsal side, and is often so greatly developed that the foot itself appears as an appen- 
dage. The protrusion of the organ, at least in most of the examples that I have noticed, 
is by the eversion of the integuments. When these are evolved to the utmost, the organ 
is seen to be a thick column, conical or nearly cylindrical, \vith the extremity trmicate, 
and surrounded by a wreath of vibratile cilia. It was, doubtless, the extremity of the 
penis that M. DujARbiN saw, as “ un organ cilie entre les muscles de la queue A in the (so- 
called) Enteroplea. The male of Sacculus viridis (flg. 26), a species which is footless in 
* Beightwell iu ‘ Ann. Nat. Hist.,’ Sept. 1848. f Op. cit. p. 32. 
