26o SOME RECENT 



blastomeres. These follicle cells, or kalymmocytes 

 as they are called by Salensky, are at first very 

 distinct in appearance from the blastomeres, and 

 easily recognised from these ; but as development 

 proceeds the differences become less and less 

 marked, and finally cease to be evident. These 

 ingrowing follicle cells, or kalymmocytes, enter 

 directly into the formation of the embryo, which is 

 thus built up partly from cells derived, as in other 

 Metazoa, from division of the fertilised egg or 

 ovum ; and partly from cells of independent origin, 

 the kalymmocytes, which are unfertilised, and have 

 grown into the egg from the surrounding follicle. 

 In the genus Salpa a similar condition of things 

 has been described by Salensky ; the only difference, 

 as compared with Pyrosoma, being that in Salpa 

 the kalymmocytes are actually more numerous and 

 more bulky than the blastomeres formed by seg- 

 mentation of the ovum, so that the major part of 

 the embryo is composed of unfertilised cells. 



These observations are of the greatest possible 

 interest, and we wait anxiously to learn whether 

 this curious mode of development is confined to the 

 groups of Ascidians, or whether it occurs in other 

 animals as well. It is perhaps worth while 

 suggesting that if the process were carried one 

 stage further than it actually is in Salpa, we should 

 arrive at a condition of things curiously resembling 

 the mode of formation of gemmules in Sponges, or 

 of statoblasts in Polyzoa. In Pyrosoma, the follicle 

 cells or kalymmocytes form part, but the smaller 

 part, of the embryo. In Salpa, the kalymmocytes 



