Il(j4 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The author refers to the observations of some recent workers on 

 corals, lie urges that he has made sufficient observations on the epithoca 

 of Astroides, ami that Mr. G. C. Bourne's lament is unnecessiry. He 

 docs not rLmnin silent under Mr. Bourne's treatment of his diagram of 

 the epithcca. There are also replies to other criticisms by Mr. Bourne 

 and Dr. G. H. Fowler, all of which are, to use tlie author's own expres- 

 sion, " polemisch." 



Sexual Cells and Early Stages in Development of Millepora 

 plicata.* — 1 >r. S. J. Hickson, who has already noted that a species of 

 Milhpora is hermaphrodite, has been continuing his investigations. 

 Both male and female cells arise in the ectoderm of the coeuosavcal 

 canals which anastomose between the dactylozooids and gastrozooids ; 

 the youug ova become spindle-shaped and penetrate the mesogloea to 

 enter the endoderm earlier tlian the spermatospores. As soon as the 

 latter have taken up their position in the endoderm their nucleus 

 increases considerably in size, the protoplasmic meshwork splits up into 

 a number of hook or rod-shaped pieces, and then divides again into a 

 large number of very small particles. The male spores now migrate 

 along the canals to the zooids, in most cases choosing the daetylozooids, 

 but occasionally the gastrozooids ; and they pass iuto their cavity, which, 

 by the disappearance of the surrounding membrane of the spermatospore, 

 is occupied by a swarm of young spermatoblasts. Again entering the 

 endoderm, they push out the mesogloaa into a number of diverticula 

 between the tentacles, in which they remain till they are mature ; these 

 diverticula, or sporosacs, vary considerably in number. As the author 

 was unable to find any trace of the formation of the sporosac before the 

 advent of the spermatoblasts he thinks that these must be the active 

 agents in the formation of the sporosacs ; or that, in other words, they 

 do not migrate to any locality or structure ali'cady prepared for them, 

 but choose for tbemselves localities which can readily be pushed out in 

 the form of sporosacs. 



As the ova increase in size they become stalked, the stalk remaining 

 attached to the mesogloea; this stalk is not a separate structui'e, but 

 merely a pseudopodium modified for the purpose of retaining the ovum 

 in position. Two polar globules are successively given off. During 

 the formation of the second spindle, and subsequently, the substance of 

 the ovum becomes clouded and heterogeneous, as if some considerable 

 disturbance of the protoplasm was going on. After impregnation the 

 ovum again becomes clear and homogeneous ; the nucleus, soon after its 

 reappearance, is seen to be filled with a number of small spherical bodies 

 like nucleoli ; the wall of the nucleus next disappears, and then spherical 

 bodies, together with a number of very small fragments, are seen 

 scattered about in that region of the ovum which was formerly occupied 

 by the nucleus ; later on, they migrate and form an equatorial zone of 

 two or three rows : this zone divides into two clusters of fragments, 

 which are eventually scattered over the whole ovum. Favourably 

 stained specimens show that each fragment is surrounded by its own 

 proper protoplasm ; this is the morula stage, which is succeeded by a 

 solid blastosphere. The embryos are then, probably, set free into the 

 sea as ciliated larvae. 



The migration of the sexual cells into the endoderm may be ex- 



♦ Piiil. Trans., clxxix. B. (18S8) pp. 193-204 (2 pis.). 



