334 SUMMARY OF CURRENT RKSEARCHES RELATING TO 



they require favourable environment. A pedigreed strain has been bred 

 for 102 generations. By selection a striking increase in the percentage 

 of twins may be produced. The division rate is similar to that of normal 

 single animals. As pairing, cannibalism, and twin-formation occur 

 among animals in a similar physiological condition, it is believed that the 

 three phenomena are but expressions of an abortive attempt to undergo 

 syngamy, abortive probably because of the absence of idiochromatin 

 morphologically segregated as nuclei. J. A. T- 



Life-History of Myxidium gadi. — Jivoin Georgevitch {Arch. 

 Zool. Exper., 1919, 58, 251-89, 3 pis., 3 figs.). Monosporic, disporic, and 

 polysporic forms occur. In all cases, however, the scheme of the life- 

 history is the same. At the end of sporulation a syncarion is formed, 

 and this unicellular stage (zygote or pansporoblast resulting from the 

 total union of two isogametes) is at the start of each new developmental 

 cycle. This zygote does not immediately enter upon sporulation : it 

 passes through several generations of similar schizonts before becoming 

 sporont. There is always alternation of generations between schizogonic 

 forms and sexual sporogony. Schizogony is marked by equal cell- 

 divisions ; in sporogony there are two unequal divisions of the nucleus 

 alongside of equal divisions. After several generations of schizogony, the 

 details of which are described, the schizonts enter into sporogony. If 

 the schizont is monosporic or disporic, the first division of its nucleus is 

 unequal, unlike the subsequent divisions. If it is polysporic all the 

 divisions are equal. The diverse phases of the monosporic, disporic, 

 and polysporic operations are dealt with, all of them leading eventually 

 to a zygote. At no stage are these parasites intracellular. J. A. T. 



