On the Structure of the Stylasteridae. 189 



The gonophores are sometimes single in the ampullae, sometimes 

 in groups of two or three arising from a common base with 

 their contents in various stages of development. The ripe sper- 

 mato/.oa are precisely similar in form to those of Garveia nu- 

 tans *. In Allopora, Acanthopora, and Stylaster eruhescens the male 

 gonophores have a similar structure. In the Stylaster allied to 

 Cryptohelia the male elements are developed in a series of sacs, 

 which encircle the calicle, often in a double row. The sacs spring 

 from the coeuosarcal network ; they contain numeroixs smaller glo- 

 bular cysts, attached to a common basal endodermal tissue. These 

 cysts are some of them filled with ripe spermatozoa, others with 

 spermatic cells in various stages. The female gonophores are, 

 in Errina, simple, i. e. each ampulla contains only a simple ovum 

 or embryo. In Cryptohelia large sacs are present at the sides of 

 the calicles, which contain ova and embryos in all stages of develop- 

 ment. Only a single sac of the kind is developed in relation with 

 each calicle. In both genera the spadix in its earliest stage is cup- 

 shaped, the cup having fitted mto it an ovum with germinal vesicle 

 and spot well marked. The ova early lose the germinal vesicle 

 and spot, and develop into very large planulae, in the same manner 

 as, e. g., those in Laomedea /lexuosaf. In Errina the planuloe are 

 more ovoid in form than in Oryptohelia, in which they are long 

 and worm-like, measuring ^ of an inch in length. They have a thick 

 transparent ectoderm, abundantly supplied with the larger form 

 of thread-cells. The spadix in both genera, as the development of 

 the ovum proceeds, becomes divided at its margin into a series of 

 lobes, which lobes subdivide and encroach over the surface of the 

 ovum until more than half the pi'oximal surface of the ovum is 

 thus embraced by the cup of the spadix. The lobes of the margin 

 of the spadix appear just like developing tentacles ; and the spadix 

 of Cryptohelia was at first supposed to be a developing actinula. 

 The outer, thin, perforated calcareous walls of the ampullae in 

 Errimi appear to get thinner as de\'elopment of the embryo ad- 

 vances, until they fall away or are absorbed altogether, and give 

 free exit to the planula. In Cryptohelia the planulae probably 

 escape through the mouths of the calicles. The endoderm, spa- 

 dices, &c. are coloured red by a colouring-matter, soluble in spirit, 

 insoluble in glycerine, in Polypora, Cryptohelia, and Errina. In 

 the Stylaster resembling Cryptohelia the coloration is dusky green. 

 The green colouring- matter is soluble in spirit, and yields an ab- 

 sorption-band in the spectrum. In Polypora the living layer of 

 coenosarc set free by decalcification is very thick, not merely a 

 thin superficial film as in Millepora ; indeed all bub the most cen- 

 tral axial regions of the branches of the corals are in active life. 

 In the other genera the whole of the coral appears to maintain 

 its vitality, there being no dead region represented by a cavity 

 after decalcification. 



* ' A Monograph of the Gymnoblastic or Tubularian HydroidB,' by G. J, 

 Allman, M.D. &c., Ray Soc. part 1, pi. xii. fig. 9. 

 t Allman, /. c. p. 86. 



