576 BULLETIN OF THE 



pronucleus. In Sagitta bofh are " open " on the side toward the centre of the 

 aster, and in Limax both are drawn out in the same manner, and their out- 

 lines become less conspicuous on the side toward tne aster. But while Fol 

 represents the line which indicates the contour of the pronucleus in Sagitta as 

 terminating rather abruptly, I have simply seen the outline become very 

 gradually less distinct, but never wholly interrupted. The pronuclei in Limax 

 present the same smooth, even contour on the side toward the aster as else- 

 where ; it is only less conspicuous, not less precise, on that side.* There is, 

 besides, this difference in the two cases : in Sagitta the aster arises in connec- 

 tion with the male pronucleus, but in Limax in connection with the female. 



At this stage (PL X. Fig. 7), continues the author, a corpuscle is generally 

 seen suspended in the liquid of the cavity of each of the vacuoles, near 

 the side with which they are about to come in contact. They are very dis- 

 tinct, owing to the low refractive power of the liquid, and are comparable to 

 the nucleoli found in the pronuclei of other animals. The pronuclei have 

 the form of a grape from which the stem has been torn ; it is by this trun- 

 cate side that they approach each other, separated by only a thin layer of 

 vitelline substance. Some of the rays of the aster now converge toward 

 the space which separates the two pronuclei, and the others toward the infe- 

 rior t extremity of the male pronucleus. When the pronuclei meet, the rays 

 extend around both, converging toward the line which separates them. In 

 coupling, they are mutually flattened. FoFs Fig. 10 seems to indicate that 

 they are no longer " open " when this flattening begins. They always deport 

 themselves optically, he continues, like vacuoles full of liquid in the midst 

 of a denser substance. The contours are perfectly distinct, but simple and 

 without indication of a membrane or limiting layer. Variable sarcodic masses 

 are visible within the pronuclei. The rounded mass (nucleolus) of the pre- 

 ceding stage has disappeared, and in its place are seen sometimes filaments, 

 sometimes partitions, at other times streaks of sarcode stretching across the 

 cavity in various directions, and exhibiting enlargements of all forms and sizes. 

 The stars of the first cleavage amphiaster evidently arise in Sagitta, also, be- 

 fore the fusion of the pronuclei ; for the author says that, when considerably 

 flattened, there often appear at their opposite lateral edges small lenticular 

 masses which project into their cavity. (Compare loc. cit., Taf. X. Fig. 9.) 



The corresponding events in the Heteropoda offer many points of resem- 

 blance with Limax. In one place the author speaks incidentally of the mul- 

 tiple condition of the female pronucleus. When it is composed of two or three 

 small nuclei, each of them, he says, contains its own nucleolus. The figure 



* From the difficulty of rendering a sharp outline on stone with the crayon, the 

 pointed ends of the pronuclei in Fig. 68 are not quite so definite, especially in the 

 later prints, as they should be. 



t From the figures cited it is evident that the blunt end of the pronucleus is 

 meant, although it is ujjp&rmost in the figure. The description may date from a 

 period before the author began to deviate from the customary method, by placing the 

 vegetative pole of his figures uppermost. 



