REPORT ON CORALS — HYDROCORALLTN^E. 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 (PI. 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 coenosarcal mesh- 

 work, the endoderm of the spadix being continuous with that of these canals. 



Pliobothrus, Pourtales. 



The genus Pliobothrus was formed by Pourtales (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. Pourtales 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 

 symmctricus 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 Stylasteridse, namely, Cryptohelia, Stylaster, 

 and Disticho2)om, The structure of the soft parts of Pliobothrus proves the coral to 

 belong undoubtedly to the Stylasteridse. The specimens of Pliobothrus syrnmetricus 

 examined by me were dredged off Florida Eeef, in 100 to 300 fathoms. 



