REPORT ON CORALS—HYDROCORALLIN AE. 47 
The gonophores are composed of a spadix, which is extremely conspicuous in the fresh 
condition of the tissues, because it is full of red endodermal cells and thus deeply pig- 
mented, and a mass of testis cells or spermatozoa. The spadix is cylindrical in form, with 
a rounded extremity. It occupies the axis of the deeper region of each gonophore. It 
thus forms the core of the spheroidal body, the remainder of the mass of which is com- 
posed of spermatozoa or the cells from which they are developed in various stages of 
advancement. These cells and spermatozoa are contained within a fine and transparent 
but tough membrane which invests the whole body of the testis, being derived from the 
ectoderm. I believe that a layer of the ectoderm invests the spadix within the testis, but 
am not certain. I could not determine from which layer the spermatic cells are 
developed. 
The spermatozoa are developed in the same manner as in other Hydroids. In 
Plate III. G, is figured the usual mass of small spermatic cells in an unripe testis. 
Above this is a ripe testis which is shown as not cut right through its axis, it being 
bent over a little from the perpendicular to the surface. Hence the spadix is not seen in 
the section. 
The ripe spermatozoa (Pl. X. fig. 12) have conspicuous heads which are elongate 
bodies curved into a bow shape. They are compressed and flattened in the plane of the 
curve, so that though broad and conspicuous when viewed on the flattened sides they 
appear almost linear when seen on edge. At the extremity of the head where the tail is 
attached, a small rounded vesicle was observed in all cases to be present. 
The bases of the gonophores are continuous with large canals of the ccenosarcal mesh- 
work, the endoderm of the spadix being continuous with that of these canals. 
Pliobothrus, Pourtalés. 
The genus Pliobothrus was formed by Pourtalés (Bull. Mus. Comp. Zool., Cambridge, 
Mass., No. 7) to include specimens dredged by the United States’ Coast Survey off the 
coast of Florida, in from 100 to 150 fathoms. Pourtalés rightly placed the new genus 
amongst the Hydroids, but, judging from the structure of the hard parts alone, associated 
it with Millepora. He most kindly placed at my disposal specimens of Pliobothrus 
symmetricus preserved in spirit, and in excellent condition; and these have yielded 
tolerably complete evidence as to the structure of the soft parts, Moreover, the two small 
specimens transmitted to me proved to be of opposite sexes. I have observed both sexes 
only in the case of three other genera of the Stylasteride, namely, Cryptohelia, Stylaster, 
and Distichopora. The structure of the soft parts of Pliobothrus proves the coral to 
belong undoubtedly to the Stylasteride. The specimens of Phiobothrus synumetricus 
examined by me were dredged off Florida Reef, in 100 to 300 fathoms. 
