ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 359 



(the " marginal corpuscle ") which during division disposes itself in the 

 equatorial plate with the nuclear threads and divides there ; its halves 

 move behind the daughter plates towards the poles and form the 

 marginal corpuscles of the daughter nuclei. 



Cnidocysts of Peridinids.*— E. Chatton gives an account of these 

 structures in Polykrikos schivarzi Biitschli. He finds that this form, 

 occurring on the European shores of the Atlantic, is specifically distinct 

 from that described by Kofoid for the American coast of the Pacific, 

 and he therefore names the latter P. kofoidi. The Atlantic species 

 P. schivarzi is found also in the Mediterranean. Its cytoplasm has 

 trichocysts which are inconstant, and cnidocysts which are constant. 

 The cnidocysts are fundamentally similar in structure to those of 

 Ccelenterates, and they are discharged by a similar mechanism, with the 

 difference that the filament does not uncoil as it is evaginated. The 

 cnidocysts are not discharged by the intact Polykrikos, which does not 

 appear able to control their explosion. In the Polykrikos the cnidocysts 

 go through a series of stages which constitute a true developmental 

 cycle. They multiply by autogenesis ; a cnidoplast differentiates into 

 a cnidogen, which reproduces a cnidoplast, which, by chitinization, 

 becomes a cnidocyst. The element thus exhibits a phase in its develop- 

 ment in which it grows and reproduces (cnidoplast — cnidogen), and a 

 phase in which it simply undergoes chitinization. The finished cnido- 

 cyst is nothing more than an inert mechanism. The nuclei of the 

 Polykrikos take no share, direct or indirect, in the formation of the 

 cnidocyst. The ampulla (corresponding to the spiral tube of the 

 nematocyst of Ccelenterates) is formed independently of and before 

 the capsule. The filament grows, like a fiagellum, in a vacuole starting 

 from a chromatophilous granule which may be centrosomic. The cnido- 

 cysts of P. schivarzi are intrinsic ; they are not of alimentary origin, 

 nor are they parasitic. There is nothing to show that they are genetic- 

 ally allied to the trichocysts of Polykrikos, but their power of exploding 

 from the cnidoplast stage onwards, and their structure at that stage, are 

 strong arguments in favour of the cytological homology of the two. 

 The structure of the cnidogen and the mode of origin of the filament 

 seem to show that the stinging element represents a much modified 

 kineto-flagellar apparatus. 



New Schizogregarine.f — D. Keilin describes Gaulhryella aphio- 

 chsetse g. etsp.n., from the intestine of a Dipterous larva (Aphiocheeta 

 rvfipes Meig.). The schizogony is extracellular, and occurs in the form 

 of little barrel-like groups of sixteen merozoites. Each gamont produces 

 eight gametes. There are eight sporocysts, each giving rise to eight 

 sporozoites. The type requires a new family (with eight spores) between 

 Monosporea and Polysporea. In its extracellular schizont it approaches 

 Ophryocystidffi or Schizocystidre. In its grouping of merozoites it 

 approaches Selenidiida? or Merogregarinidae. 



* Arch. Zool. Exper., liv. (1914) pp. 157-94 (1 pi.). 



t C.R. Soc. Biol. Paris, lxxvi. (1914) pp. 768-71 (12 figs.). 



