190 THE MASTIGOPHORA 



jugation, they attach themselves at the peristomial region and 

 gradually fuse together to form a zygote having twice the normal 

 volume. The fusion of the nuclei of the conjugants has been 

 observed directly, under the microscope, by Cienkowski and later 

 by Plate. 



It seems likely, although still awaiting demonstration, that the 

 production of swarm-spores (zoospores) by exogenous budding 

 depends upon previous conjugation. 



The production of buds is limited to a particular area of the 

 sphere, namely, the area corresponding with the peristomial region 



where the central protoplasm is massed. 

 The cleavage of nucleus and protoplasm 

 proceeds in a manner analogous to the 

 discoidal cleavage of a yolk -laden egg 

 (Biitschli). Nearly all the parent pro- 

 toplasm is used up in the formation of 

 FIG. H. the buds, the full number of which 



Two ripe spores of NoctUuca amOUlltS to 512. 



rn iliaris, showing n, nucleus ; /, rpu i, c i i 



b, the body interpreted Ine phenomena ol karyoKinesis in 



P resent some interesting 



features. There is outside the nuclear 



membrane, but in the neighbourhood of the nucleus, a relatively 

 large archoplasmic body. Before division of the nucleus occurs, 

 this body elongates to assume a dumb-bell shape (Fig. 3, A), with 

 an aster at each end The chromatin of the nucleus concentrates 

 into a number of elongated moniliform chromosomes, and then the 

 nucleus warps itself round the central part of the archoplasmic 

 body, forming a spindle-like body round the achromatic spindle of 

 the archoplasmic body (Fig. 3, B). Finally, the chromosomes 

 divide into two parties, which travel to the opposite poles of the 

 spindle, and then both nucleus and archoplasm divide transversely. 



The buds project from the surface of the body, but remain 

 attached to it until all have attained a certain size, and until each 

 has acquired its flagellum, which represents the cilium of the adult 

 NoctUuca. 



The detached free-swimming buds have a dinoflagellate appear- 

 ance, and it may be broadly stated that the blastogenesis of 

 NoctUuca results in the formation of gymnodiniform young (Fig. 

 14). The growth of the young into the adult condition has not 

 been observed. 



The sub-class contains only three genera: NoctUuca, Suriray, 0'3-1'25 

 mm., probably cosmopolitan; Leptodiscus, Hertwig, 0'6-1'5 mm. ; and 

 Craspedotella, Kofoid (8), 0-15 -O'l 8 mm. E. Pacific. Craspedotella has 

 a strong resemblance to a craspedote medusa in form, being bell-shaped 

 and having a distinct velum at the margin. 



