370 W. K. BEOOKS OX THE LIFE-HISTORY 



his knowledge of the fact that Fritz Miiller and Haeckel had observed similar prolifer- 

 ating Cunina larva' in the stomachs of Geryonids. 



In 1875, Uljanin (60, (51) proved that there is no genetic connection between the 

 Geryonid and the Cnnina larvae (bund in its stomach, but that they gain entrance from 

 outside and then multiply asexually, and that they are sometimes found on the inside 

 of the bell, as well as in the stomach. He does not refer to McCrady, whose papers 

 were published twenty years before, but he shows that the history of the parasitic larvae 

 found in Carmarina is essentially like that of the one which McCrady had found in 

 Turritopsis. 



There is one interesting difference, however, lor in his species the original larva never 

 becomes a medusa, but permanently retains its larval nature, budding oh' numerous 

 larva:' which become medusae, lie calls attention to the fact that this is a true alter- 

 nation of generations, the egg-larvae being the first, and the larvae which are budded 

 from it the second generation. 



This discovery, and his verification of McCrady \s discovery that the larvae are parasites, 

 entitle his paper to an honorable position, but I cannot believe that his account of the 

 minute structure and of the mode of development of the larva is correct, as it conflicts 

 with all our knowledge of the subject. He says that the tentacles are developed on 

 the edge of the mouth, that the buds are formed at the oral end, that the digestive 

 cavity is formed by a peculiar infolding and splitting of the endoderm, and he figures 

 the embryo as a two-layered gastrula, with an aboral month which lias nothing to do 

 with the definitive mouth of the larva; and as this account cannot be reconciled with our 

 general knowledge of the subject, or with the careful observations which Metschnikoff 

 made (52) several years later, I am compelled to believe that he has failed to interpret 

 his observations correctly. 



In the same year, 1875, Schulze showed (58) that there is no organic connection 

 between the Geryonid and the larvae found on its gastrostyle, and he therefore decides 

 that the Cunina embryo originates outside the Geryonid, and after fastening itself to 

 its gastrostyle, gives rise to new larva' by budding, as Uljanin also shows to be the case. 



In December, 1881, Metschnikoff published an illustrated paper (52), in which he 

 traced the embryology of the parasitic larva found in Carmarina, showing that the group 

 of medusa-buds is formed by budding from the aboral surface of a ciliated egg-embryo, 

 which gains access to the digestive cavity and there multiplies asexually. In this species, 

 Cunocantha parasitica, Haeck., the egg-embryo, which in all probability corresponds to 

 the mother bud of Cunina rTiododactyla and to the larva shown in our figure 1, is very 

 much degraded. It fastens itself to its host by means of pseudopodia which are thrown 

 out at the oral end from a very peculiar large cell, which fills its digestive tract. It 

 develops tentacles, hut never acquires an umbrella or a proboscis, and soon begins to 

 produce medusa-buds from an aboral stolon. 



As Uljanin has shown, it does not become converted into a medusa, but is simply a 

 nurse for the production of medusa-buds. This species therefore presents an example 

 of a true alternation of generations, since the embryo which hatches from the egg re- 

 mains as a larva and never becomes a medusa, although it gives rise to buds which do 

 become medusae. 



