272 Proceedings of the Royal Physical Society. 



the advent of the macula within the vesicle ; and, lastly 

 the formation of the enclosing membrane. 



On examining a great number of specimens of Gromia, 

 Miliolina, Botalina, and Orbulina, I have repeatedly dis- 

 covered bodies which correspond in all respects with the 

 " primitive ovum" defined above. They consist of trans- 

 parent spheres or ovoids formed of a finely molecular sub- 

 stance, but in which the molecules are masked or rendered 

 indistinct by the highly refractive matter in which they are 

 imbedded. No germinal vesicle or spot appears in the living 

 specimens. It may be masked in a similar manner to the 

 molecular structure ; but in a specimen of Truncatulina 

 (PL IX. fig. 6) which has been hardened in spirit, decal- 

 cified by dilute nitric acid, and mounted with strong heat in 

 Canada balsam, four of the segments or zooids contain each 

 an ovum which shows a germinal vesicle and spot with the 

 utmost distinctness, while the rest present the usual appear- 

 ance of granular, low-refracting sarcode.* 



I have not been able to trace the development of the ova 

 of Ehizopods. Bodies similar to those I have considered 

 ova in Gromia are found attached to Algae in vessels where 

 that animal abounds. The ova of Gromia are very small ; 

 and young Gromias slightly larger than the ova also occur. 

 In Gromia, therefore, the ova may be at once transformed 

 into young, and directly acquire an envelope. Such is the 

 mode of development in the ova of most of the Hydroidse, 

 which are transformed into planuloid larvae without under- 

 going fissure. In Orbulina, however, the ovum is of very 

 large size, and consists of a colourless spherule' of sarcode 

 enclosed in a membraneous test and covered by a thin glairy 

 layer. Here the sarcode presents traces of fissure, though 

 these are lost when it is pressed out of its envelope. In both 

 this genus and Truncatulina it is impossible that the full- 

 sized ova can obtain exit from the animal, except by the 

 destruction of the chambers of solid shell in which they are 

 enclosed. In the case of Truncatulina, moreover, the ova 

 are at least ten times as large as the primordial segment or 



* I shall be happy to lend this preparation to any gentleman who may take 

 an interest in it. 



