74 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



and the vas deferens opens into the oviduct instead of the atrium, 

 these organs occupy the same relative position as in the adult. 



The second species is Chelyosoma productum, Stimpson ('64, p. 

 161). Here the structure is similar, but not identical, to that 

 described by Floderus (p. 187) for the genera Ascidia, Ascidiella, 

 and Corella. The ovary is much branched, occupying the superficies 

 of the viscera, and also extending in between the stomach and intestine 

 and covering their deeper surface. In each lobe, however, the con- 

 ditions are different from those in the genera mentioned, in that the 

 germinative epithelia are in two strands, which are usually entirely 

 separated from each other except at the ends of the lobes, where they 

 fuse. In the great majority of cases, especially where the lobes are 

 superficial, they are so flattened that they are parallel to the surface. 

 One of the walls thus formed, which is usually the superficial one, 

 has its median part formed of a cubical epithelium with long cilia, and 

 on both sides of this are situated the germinative epithelia with the 

 largest ova away from the median line. Occasionally the germinative 

 epithelia are broad enough to reach the lateral edges, but these are 

 usually formed by the ova that are just large enough to extend beyond 

 the wall of the ovary. The other wall is made up of the same kind 

 of ciliated epithelium, and to it all the follicles of the older ova are 

 attached. Here again, then, we have the essential structure of 

 Clavelina and Styelopsis, but developed in each of the lobes of an 

 irregularly branching ovary. It must be said, however, that although 

 the structure of the two walls is quite constant, their position with 

 respect to the surface of the animal is somewhat irregular. The posi- 

 tion is most constant in the superficial lobes, but even here only about 

 76% have the wall containing the germinative epithelia superficial, 

 while in about 14% it occupies the deeper position; and in the other 

 10% the plane of the lobe is approximately at right angles to the 

 surface. In the lobes that extend between the stomach and intestine, 

 and over their deeper side, the variation in orientation is still greater, 

 depending more upon the adjacent organs than upon the surface of the 

 animal. 



c. General Considerations. 



Floderus (p. 250) established the law that in forms with bilateral 

 arrangement of the germinative epithelia the development within the 

 same takes place from without inward. In general this holds good 

 for the three species studied, though some exceptions are encountered. 

 It would be equally true to extend the law from the germinative 



