CONTRIBUTIONS ON THE MORPHOLOGY OF THE 



ACTINOZOA. 



II. ON THE DEVELOPMENT OF THE HEXACTINI.E. 

 J. PLAYFAIR McMURRICH. 



For the past few years I have been endeavoring, as occasion 

 offered, to obtain the material necessary for the study of the 

 development of some Hexactinian, but my efforts have been only 

 partially successful. In 1887 I obtained at Nassau, Bahama 

 Islands, W.I., a few embryos of two different Actiniaria, — 

 Aulactinia stelloides, McM. and Rhodactis Sancti Tho^ncB (Duch. 

 and Mich.). Both these forms, however, retain the embryos in 

 the interior of the body until the mesenteries have formed, the 

 embryos from Aiilactinia possessing, when extruded, from eight 

 to twelve perfect mesenteries, while those from Rhodactis are 

 extruded somewhat earlier, while they are furnished with only 

 two or four perfect mesenteries. These forms, therefore, agree, 

 as regards the retention of the embryos, with the majority of 

 forms whose embryology has been studied. 



There are some forms, however, in which the ova are extruded 

 unfertilized. Adamsia parasitica is one of these according to 

 Kowalewsky ('75), and I have found that Metridimn margi- 

 natum, so abundant on the New England coast, does so like- 

 wise. During the summer of 1889, aided by the generous 

 enthusiasm and energy of two assistants, I was able through 

 the facilities offered by the Marine Biological Laboratory at 

 Woods Holl, Mass., to collect and keep large numbers of this 

 Actinian in aquaria, and so obtained some ova which were 

 artificially fertilized by sperm extruded by other individuals at 

 the same time. Unfortunately spermatozoa were not always 

 obtainable when required, and consequently I was obliged to 

 allow a large number of ova, obtained at various times, to decay, 

 and was only successful in rearing embryos in a very limited 

 number of cases. There are consequently many gaps in my 

 observations, which might readily have been filled in by the 



