144 SIDNEY F. HARMER. 



number of the nuclei^ and the mass was constricting off secon- 

 dary embryos on all sides^ and was further surrounded by a 

 good many young secondary embryos of about the same size as 

 those which were still in connection with itself. 



Demonstrative evidence of the occurrence of embryonic 

 fission during the early part of this stage was obtained in both 

 T. plumosa and in T. phalangea. In the case of the best 

 series of sections obtained of the latter, the species was not 

 merely inferred from the absence of excretory vesicles in the 

 tentacles, but had been determined, before decalcification, by 

 the characters of the ooeciostome. It appears to me that the 

 nutritive tissue is much more abundant during this stage in 

 T. phalangea than in T. plumosa. 



The younger ovicells in this stage contain a large number of 

 young secondary embryos, all in about the same stage as those 

 which are being constricted off from the larger embryonic mass 

 already described. Comparing the entire embryophore to a 

 hand, the secondary embryos at first occupy the part which 

 corresponds to the palm, where they form a dense mass, com- 

 posed mainly of secondary embryos, which are separated from 

 one another by a certain amount of nutritive tissue. Measure- 

 ments made of this mass, in sections cut in a suitable plane, 

 gave 250 — 560 ju as its greatest transverse diameter in par- 

 ticular cases. 



As in Lichen op or a, I am not able to say how far a secon- 

 dary embryo, once formed from a larger embryonic mass, is 

 capable of further fission. In some cases this process seemed 

 to be clearly indicated. But even in the oldest ovicells, con- 

 taining mature larvEe, ready to escape, and even actually in the 

 tube of the ooeciostome, I have in one or two cases found larger 

 masses of embryonic tissue clearly giving rise to more than 

 two or three secondary embryos. One of these masses noticed 

 in an old ovicell was 90 /x long, which is about the same as 

 the average length of a larva ready to escape from the ovicell. 

 The dividing embryonic masses are similar to those of Crisia, 

 consisting of a more or less clearly defined outer layer of cells, 

 surrounding a central solid mass containing specially large 



