August 7, 1879] 



NATURE 



341 



within the body of a single polyp, whereas the so 

 similar-looking radiating plates in the case of the 

 cyclosystem are skeletal plates developed outside the 

 bodies of the numerous component polyps altogether, 

 and separating a number of adjacent polyps from 

 one another. The peculiar radiate form of the cyclo- 

 systems of the Stylasterids has no doubt been gradually 

 developed as the result of the constant bending inwards 

 of the dactylozooids in each system to reach their 

 gastrozooid when further and further retracted within its 

 pore. The dactylozooids have thus in course of genera- 

 tions pulled the mouths of their pores out into the form 

 of slits all directed inwards towards the gastropore in 

 each system. In the case of some genera the gastrozooids 

 have carried matters so far that they have ceased to be 

 retracted within their own pores when at rest, but double 

 themselres inwards for safety within the wide mouths of 

 their gastropores. In one genus (Cryptohelia) a further 

 protection is afforded to the zooids by the growth in front 

 of each system of a delicate lid-like lamina of hard coral 

 skeleton, which projects in front, and shields all the 

 zooids when retracted. 



In some genera of Stylasterida; the zooids are not 

 gathered into cyclosystems at all, but various other com- 

 plications occur. Thus, in some genera there are two 

 kinds of dactylozooids, larger and smaller. The larger 

 and longer, in order to gain more reach in procuring food, 

 are borne at the tips of long spine-like projections of the 

 hard skeletons of the corals, whilst the smaller dactylo- 

 zooids are lodged in small pores at the bases of these 

 spines where they are in close proximity to the gastro- 

 zooids. The larger dactylozooids presumably catch the 

 food, and are helped in delivering it to the gastrozooids 

 by their shorter companions. 



As before stated, the mode of generation of the Mille- 

 poridas is as yet unknown, but it is certain that it differs 

 in one important particular from that of the Stylasterids. 

 In these latter small cavities, or brood pouches, termed 

 ampulke, are formed in the hard skeleton of the coral, 

 and in these the generative elements are developed. 

 Each coral stock is of separate sex, all its components 

 being either male or female. The walls of the ampulla; 

 in many cases project above the surfaces of the corals, 

 and are especially prominent in female stocks, since they 

 have in these cases to contain large embryos. In some 

 specimens of Stylasterida; the ampulte are very con- 

 spicuous to the naked eye, looking like small convex 

 blisters closely packed on the surfaces of the coral 

 branches. They are particularly well marked in the case 

 of female stocks of species of Distichopora, which arc thus 

 especially serviceable for class demonstration, and when 

 the generative function of the ampullse is premised, afford 

 evidence at a glance of the hydroid nature of the Stylaste- 

 rids. The ova are developed within the ampulla: to the 

 condition of mature planuls, when they are set free by the 

 gradual thinning and final rupture of the ampullar walls 

 and swim off" to start fresh colonies. It is highly probable 

 that the masses of tissue from which the ova are deve- 

 loped, and which protect them during growth, are repre- 

 sentatives of polyps, which have, like the dactylozooids, 

 lost their mouths, and have come by restriction of function 

 to be mere egg-bags as it were. 



In all the Stylasterids, even those with very complex 

 cyclosystems, there is a complete circulatory connection 

 between the different systems and all parts of the colony, 

 as well as amongst the components of each system. Thus 

 in these complex mutual benefit associations, certain 

 members of the colonies catch the food, but do not eat it, 

 others receive it from them and nourish the whole colony 

 thereby, whilst others again neither catch food nor eat it, 

 but devote themselves entirely to the production and 

 rearing of the young. 



The ancestral forms from which the Hydrocorallinx 

 have been developed must have been colonies closely 



similar in essential structure to their present descendants, 

 but with all their component zooids provided with mouths 

 and generative organs, all alike catching food and digest- 

 ing it, and possibly all taking their share in the production 

 of young. In such colonies further development may be 

 conceived of as having arisen by either of two processes. 

 All the zooids may have become gradually modified, so 

 that each performed only one function and thus had 

 certain of its structures ;aborted to fit it for this special 

 end. If such be the history of the development of the 

 Hydrocorallinae then the dactylozooids are to be looked 

 on as they have been regarded throughout this paper as 

 representatives of zooids which in the ancestral condition 

 were provided with a mouth and stomach, but in which 

 these structures as well as the generative structures have 

 become rudimentary by disuse. Similarly in the case of 

 the gasterozooids the functions of prehension have to a 

 large extent been lost, and the zooids have become, in 

 some cases, mere stomachs. 



On the other hand the view may be taken that the 

 gastrozooids alone represent the original zooids of the 

 ancestral colony. They remain, having lost their genera- 

 tive organs and to a greater or less extent their prehensile 

 ones because additional zooids have been formed by 

 budding in order to provide for the wants of the colony 

 in these particulars. On this view the generative zooids 

 and dactylozooids were originally budded out in the con- 

 dition in which they now exist or in one not so complete 

 as it is at present, nor so perfectly adapted to their present 

 function. On this view they have lost no structure by 

 disuse, but have rather advanced in complexity with 

 development but only in their own specialised direction. 



The former view of the antecedent history of the sub- 

 order Hydrocorallins has been here adopted, because the 

 presence of several structures which occur as rudiments 

 in connection with the dactylozoids and generative zooids, 

 but which are fully developed in connection with the 

 gastrozooids, seem to bear out this conclusion. As 

 examples may be cited the calcareous styles which gave 

 the name to the family Stylastcridae. These styles are 

 small projections of the hard skeletons of the corals 

 which support the gastrozooids within their pores. In 

 several genera rudimentary styles are found to occur in 

 connection with the dactylozooids. 



The Stylasteridas, in the complexity of their compound 

 stocks, form an interesting parallel to the Siphonophora. 

 In the Siphonophora the several components of the com- 

 pound organisms are by the best authorities regarded not 

 as individual zooids, but as portions of the organisms 

 which, being budded out, tend in their growth to assume 

 more and more the form of individuals. The question is 

 to some extent one of nomenclature, but it must not be 

 forgotten that though the diverse elements composing the 

 organism in the case of the Siphonophora may seem 

 closely paralleled by those of which that of a Stylasterid 

 is made up, the past history of the two organisms may be 

 very different. In the one case an ancestral already 

 compound organism may have gradually modified its 

 similar zooids to subserve division of labour, whilst in the 

 other a simple ancestor may have gradually developed a 

 similar compound organism by throwing out buds of 

 various forms, which have come more or less to ap- 

 proach itself in complexity. H. N. Moseley 



JRIDO-PLA TINUM 



THE volume of ihe proch-mriaux of the International 

 Commission of Weights and Measures published in 

 Paris last year,' contains, among other matter of much 

 value, an interesting appendix by MM. Sainte-Claire 

 Dcville and Stas, who were requested by the Commission 

 to ascertain the composition of theplatinum-iridium alloy 

 employed in the preparation of the rules and cylinders 



' Gauthier-VilLirs. P.ir:s, 1S78. 



