1876.] 



Structure of the StylasteridcB . 



97 



larger cells are mostly gathered together in nematophores, which are dis- 

 posed irregularly amongst the zooids m Polypora, regularly in the inter- 

 vals between the tentacular zooids at the margins o£ the cahcles in Cryp- 

 tohelia and the Stylaster resembling it. The smaller kind of thread-cells 

 are of an ovoid form, sHghtly flattened on one side ; they occur in the 

 tentacles of the alimentary zooids, and form a closely set covering over 

 the entire external surfaces of the tentacular zooids. No three-spined 

 thread-cells, like those occurring in Mille]pora, exist in the. Stylasteridse. 

 Eeproduction takes place by means of adelocodonic gonophores, which are 

 produced as buds from the coenosarcal network without ha^dng any other 

 connexion with the other zooids. They occupy in the corallum the am- 

 puUse which in Polypora are concealed beneath the even external surface 

 of the corallum, but in the other genera of Stylasteridse show them- 

 selves as rounded prominences on the surface of the coralla, being 

 specially prominent in Errina and Disticliopora. The Stylasterid^ 

 are all dioecious. Females only of Errina and Cryptolielia^ have 

 been examined, and males only of the other genera. The generative ele- 

 ments of AcantJiopora were not observed at all. In the males of Polypora 

 the gonophores present the usual structures occurring in Hydroids ; they 

 are simple ovoid sacs, with an axially placed spadix, and resembling 

 in all respects those, e. g.^ figured by Allman from Laornedea flexiiosaf. 

 The gonophores are sometimes siugle 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 spermatozoa are 

 precisely similar in form to those of Garveia nutans t- In AUopora, 

 AcantJiopora, 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 coenosarcal network ; they contain nume- 

 rous smaller globular 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 cahcles, which 

 contain ova and embryos in all stages of development. Only a single sac 

 of the kind is developed in relation with each cahcle. In both genera the 

 spadix in its earhest stage is cup-shaped, the cup having fitted into 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 Laornedea flexuosa§. In Errina the pla- 

 nulse are more ovoid in form than in Cryptolielia, in which they are long 

 * OfiP Japan last year a small fragment of what, at tlie time, I determined to be a 

 male Cryptohelia was obtained by the dredge. I unfortunately cannot now refer to 

 the specimen. 



t ' A Monograph of the Gymnoblastic or Tubiilarian Hydroids,' by G. J. Allman, 

 M.D. &c., Ea.y Soc. part 1. p. 65. 



+ If>id. pi. xii. fig. 9. § Allman. / c.-p. 86. 



