536 SUMMARY OF CURRENT RESEARCHES RELATING TO 



are not the same in the genera in question. In Peachia these four last 

 are exoccel tentacles, and in Cribrina they are endoccel. The eight first 

 tentacles in Cribrina are the six which later form the six primary 

 endoccel tentacles plus two primary exococl ones. In Peachia the eight 

 first form the two primary endoccel (directive) tentacles plus the six 

 primary exoccel. This is related to a difference in the position assumed 

 by tentacles nine to twelve. There exist in the twelfth tentacle stage 

 of Actiniarians two types, which are already indicated in the eighth 

 tentacle stage : (1) Bilateral. On each side of the plane of direction 

 and on both sides of the ventro-lateral tentacle of the eighth tentacle 

 stage there arises an exoccel tentacle, so that the dorsal tentacle develops 

 a little earlier than the ventral. (2) Biradial. Here there appear about 

 the same time four endoccel tentacles, two on each side of the plane of 

 direction, on both sides of the lateral tentacle of the eighth tentacle 

 stage. The paper includes a consideration of transverse division in 

 Gonactinia, as well as notes on heteromorphism in the Actiniaria. 



Protozoa. 



Significance of Pigment Spots in Protozoa.* — R. Halben dis- 

 cusses the significance of the pigment in the " eye-spots " of certain 

 Protozoa, and generally the problem of " seeing " in simple Invertebrates. 

 The significance of a pigmented spot in Protozoa and in transparent 

 Metazoa he seeks to interpret in the following manner. It is capable 

 of orientating the body with respect to light. In other words, it 

 functions as a shadow giver. If parallel light strikes on a ball-like 

 mass of pigment in a transparent animal a shadow-cylinder is formed, 

 in relation to which the organism automatically seeks to orientate itself, 

 so that the shadow coincides with the long axis of the body. The 

 animal thus turns the " eye " to the light or seeks to withdraw 

 from it. 



Neogamous Gregarines.f — H. M. Woodcock gives a preliminary 

 account of the life-cycle of Cystobia irregularis and other allied gre- 

 garines, which from their constant occurrence in pairs he terms " neo- 

 gamous." C. irregularis is parasitic in Holothuria forskali. The adults 

 are perfectly regular in form and beautifully ovoid. The two associates 

 are sometimes separated by a distinct septum, and sometimes not, which 

 is dependent on the time of their union. In C. minchinii occurs one 

 of the most advanced instances of neogamy yet known, the fusion 

 taking place almost at the commencement of the life-cycle when the 

 parasites are scarcely more than sporozoites, and comprising an absolute 

 union of the two cytoplasms, the nuclei alone remaining distinct. Here 

 the fusion is longitudinal, that is, side by side ; in C. irregularis it is 

 end to end. The author regards this extremely precocious association 

 as an adaptation on the part of the parasites to ensure a suitable asso- 

 ciation, which would otherwise be rendered very difficult by the loss of 

 mobility characterising these ccelomic forms. Successive phylogenetic 

 steps in the increasing intimacy of the process are seen in Diplocystis 

 major, D. minor, and D. schneideri. 



* Biol. Centralbl., xxiv. (1904) pp. 283-8. 



f Arch. Zool. Exp et Gen., xxxii. (1904) Notes et Revue, pp. cxxv.-cxxviii. 



