282 HETEROGENETIC ORIGIN 



that Fig. 74, C, represents a later stage of development of products 

 directly traceable from the egg-substance such as are shown in 

 Fig. 76, D. The spheres are about equally numerous in the two 

 cases, and they are in each case also rather unequal in size. This 

 inequality is seen in Fig. 74, D, and also in Fig. 78, A ; and the 

 uppermost of the masses in this latter figure seems to be 

 beginning to develop into a Vorticella. 



All the spheres, in fact, which during this period were produced 

 from the Hydatina eggs developed not into Oxytrichas but into 

 Vorticellas. Over and over again in the specimens examined 

 there has been the common association of these embryo and 

 young Vorticellas with the unbroken or broken egg-cases of the 

 Hydatinas, on their removal from the dark pots. Groups of such 

 VorticellEB around egg-cases are represented in Fig. 78, B ( x 125), 

 and in one of these an undeveloped matrix is still to be seen. All 

 the stages in the development of Vorticellse from these matrices 

 have also been traced. Young organisms, having contractile 

 vesicles, and about to emerge from their own hyaline cysts, 

 are shown in Fig. 74, E (x 250), while very many of them 

 have been found with pedicles in different stages of develop- 

 ment such as may be seen in Fig. 74, F, G and in Fig. 78, B. 

 In many of the fully developed forms with expanded oral cilia, 

 and very delicate transverse strias, a slightly curved sausage- 

 shaped nucleus has also been made out. One of these developed 

 forms is shown with the aid of a weak solution of mastzellen stain 

 in Fig. 78, D (X 250). 



Again, in the spring of 1902 I had an opportunity of making a 

 few more observations upon the presence of embryo Oxytrichae 

 and their matrices within the egg-cases of Hydatinas. These last 

 observations were of this nature. In a thin Euglena pellicle about 

 nine days old, which had been kept in a very dim hght, I found, at 

 the junction of the surface of the fluid with the bowl, several small 

 Hydatina egg-cases containing the spherical matrices as well as 

 active young Oxytrichce. One of these specimens, in which were 

 contained fifteen small matrices together with one active Oxytricha, 

 is shown in Fig. 77, C ( X 200) — the Oxytricha being hidden at the 

 time the photograph was taken. I found another egg which 

 contained ten similar matrices with one small active Oxytricha ; 

 and also three small Hydatina eggs close together, each containing 

 a mixture of matrices (in some of which the Ciliates were revolving), 

 together with free and active Oxytrichas. While arranging to 



