268 DR J. H ASHWORTH AND DR JAMES RITCHIE ON THE 



sporosac appears to become gradually thicker and of deeper colour, and its coat of 

 debris also increases in amount. The length of a mature male sporosac is '17-' 19 mm., 

 and its maximum diameter "1— '13 mm. 



Although we have been unable to follow the development further and to study the 

 actual release of the sporosacs, it is evident that, as in the Neapolitan examples, the 

 cuticle, probably under mechanical tension, becomes ruptured in the neighbourhood 

 of the sporosac-neck, that the neck itself, being unable to bear the whole strain put 

 upon it, breaks, and thus the sporosac is liberated. The tentacles, on being released 

 from confinement, come to lie more or less parallel to the long axis of the body. 



Allman, in 1861 (p. 169), gave a description of the adult male sporosac, and this 

 he repeated in substance in his monograph (1872, p. 226). He gives no information 

 regarding the development of the sporosac, nor does he mention the peculiar con- 

 striction which ultimately leads to its release; indeed his figure (1871, pi. viii, 

 fig. 5) is defective in showing no trace of a constriction nor of the "defined line" to 

 which he refers as forming the breaking plane proximal to the tentacle bases. It 

 seems to us also that Allman has distorted his description and obscured the issues 

 by impressing on this unique type of sporosac a terminology derived from and 

 depending on medusoid homologies. Thus, as applied to the male sporosac of 

 D. conferta, Allman' s " internal sac" or " endotheca" is no more than the ectoderm, 

 a direct derivative, slightly modified, of the ectoderm of the blastostyle ; and the 

 " external sac " or " ectotheca " is simply the cuticle secreted by the ectoderm, 

 homologous and continuous with the cuticle which covers the ectoderm of the blasto- 

 style and of the colony in general. The assumption that the sporosac is a medusoid 

 has led Allman into a further error ; for assuming the usual construction of a medu- 

 soid to be followed in this case, he described and figured a distinct space between 

 the "ectotheca" and the "endotheca" (1871, pi. viii, fig. 5). So far as we have 

 observed, the cuticle, except for such small distortion and displacement as are 

 unavoidable in preservation and mounting, lies close upon the ectoderm, and there 

 is no determinate space between the two as represented in Allman's figure. The 

 tentacle in its growth forces apart the cuticle from the ectoderm, but there is not an 

 already pre-existing space. In his description of the release of the sporosac an 

 obvious slip occurs, for the sporosac could not break through the " endotheca," as 

 he states, but escapes from the so-called " ectotheca." 



Female sporosacs were not discovered on any of the mature colonies of D. conferta 

 examined by us. In this respect our experience agrees with that of Goette 

 (1897, p. 67), who found that colonies with female sporosacs were entirely unisexual. 

 Allman, however, states that he " occasionally met with both male and female stems 

 in the same colony" (1872, p. 226). The earliest stages in the development of the 

 female sporosacs have been described by Goette (1897, pp. 67, 68, Taf. vi, figs. 

 122-127). They closely resemble those of our Neapolitan material, except that in 

 place of the single oocyte of the latter the sporosac of the former includes two. In 



