280 HETEROGENETIC ORIGIN 



at the end of the second day showed a large number of active and 

 healthy specimens of Diglena,' and a number of young Hydatinae 

 whose development had progressed under these conditions, but 

 not a single Ciliate of any kind. Examination of another portion 

 of the pellicle at the end of the third day showed at once, to my 

 surprise, a fairly large number of small Vorticellae, all of about the 

 same size. Very soon I came upon an unruptured Hydatina egg 

 containing at least twenty spherical masses, slightly unequal in 

 size, a photograph of which is shown in Fig. 74, C ( X 250). Close 

 by the side of this was a ruptured Hydatina egg, still containing 

 five of the spheres (Fig. 74, D) ; while between the two eggs were 

 three of the small active Vorticellae. 



My suspicion that the Vorticellae had developed from the 

 spheres found in the Hydatina eggs was soon confirmed by finding 

 spheres in which the embryos were more developed and about to 

 emerge from their delicate cysts, as in Fig. 74, E. These embryos 

 showed contractile vesicles, and in the larger of the two there was 

 the usual differentiation of the oral and caudal extremities. 

 Embryo Vorticellze (unlike the young Oxytrichae) do not revolve 

 within their cysts, owing to the lack of cilia distributed over their 

 surface. Several other eggs were found in the same and in 

 subsequent specimens from this pellicle, containing similar spheres ; 

 some of the eggs being entire, and others ruptured with part of 

 the spheres discharged, as in Fig. 78, A. In each specimen also 

 there were a number of the small Vorticellae (but no other kind of 

 Ciliate) in different stages of development, such as I succeeded in 

 photographing in Figs. 78, B (x 125), C, D (x 250), after arresting 

 their movements, and slightly staining them by means of a dilute 

 solution of Westphal's mastzellen fluid. Some of the embryos 

 were seen, just emerged from their delicate cysts, exhibiting their 

 characteristic contractions of the posterior part of the body and 

 the commencing formation of the pedicle, exactly as I had seen 

 and described many years previously.^ 



Nowhere, however, could I find the early stages of this trans- 

 formation of the Rotifer's egg into many Ciliate matrices. Under 



' Specimens of Diglena have constantly been present with the Hydatinze 

 during these observations, and their eggs have frequently been taken from the 

 pots, but none of them have ever been seen undergoing changes anything like 

 those in the Hydatinae eggs. The Diglenae seem, indeed, quite to flourish in 

 the dark-pots. All batches of Hydatina eggs are, moreover, not equally prone to 

 undergo these heterogenetic changes. 



' " The Beginnings of Life," vol. ii., p. 464. 



