10 SIDNEY P. HARMER. 



of nuclei arranged in one row ; and it encloses a minute 

 central cavity. 



PI. Ill, fig. 17, represents a median section, slightly 

 magnified, of an ovicell of Crisia ramosa. The ovicell con- 

 tained in all about 115 embryos, which were embedded in a 

 loose protoplasmic reticulum, filling up most of the cavity of 

 the ovicell. In the older embryos, the conspicuous sucker or 

 " internal sac " is clearly seen ; and in some of them, a slit- 

 like space which is the mantle- cavity. The aperture of the 

 latter to the exterior is not shown in any of these embryos. 

 To the left of the ovicell is the structure from which all the 

 embryos have been produced. This structure is labelled 

 " primary embryo ;" the evidence that this name implies its 

 real nature being given in the sequel. The primary embryo is 

 produced into several processes ; and indications are seen, in at 

 least one case, that the end of the process is being constricted 

 ofi", as a rounded mass of cells, which is equal in size to the 

 smallest of the embryos found free in the protoplasmic reti- 

 culum. 



Fig. 11 (PI. II) is a longitudinal section of a young 

 ovicell, at the period when the formation of " secondary " 

 embryos (i. e. embryos which are developed by budding from 

 the "primary" embryo) has just commenced. The proto- 

 plasmic reticulum includes one or two free embryos, the 

 structure of which has already been described. The most 

 conspicuous structure in the section is, however, the large 

 primary embryo, which consists of a dense mass of granular 

 protoplasm containing numerous nuclei, and having an ex- 

 tremely embryonic appearance. This structure is in a state 

 of active growth, as is shown by the occurrence of nuclei with 

 karyokinetic figures. The proximal end of the primary em- 

 bryo is compact and rounded, and contains centrally a group 

 of nuclei which are distinguished by the activity with which 

 they are undergoing division. The opposite end of the primary 

 embryo is produced into several irregular processes, which 

 show constrictions at intervals. From the ends of two of 

 these processes, embryos have just been constricted oflP, and 



