488 
\V. A. UASWEfJ,. 
aquatic organisms must often suffer wholesale destruction as 
a result of the drying-up of the smaller streams. Crayfishes 
are able to avoid such a fate by sheltering between boulders 
or burrowing deeply in the bed of the stream. The animals 
adhering to them thus have a chance of survival denied to 
their free-living relatives. Yet it may, and doubtless does, 
often happen that even the Crayfishes are unable to escape 
the risk of desiccation. Under such cii’cumstances the 
presence of a relatively large space filled with water in the 
intei'ior of the egg of the Temnocephalese may make all the 
difference in enabling the embryo to retain its vitality until 
the dry period passes and the stream fills again. 
Literature cited. 
1. Benedeu, E. von — “ RechercJies sur la comjjosition et la significa- 
tion (le roBnf,” ‘ Mem. Acad. Roy. de Belgique,’ tome 34 (1870). 
2. Braun, M. — “ Trematodes ” of Bronn's ‘ Klassen imd Ordnnngen 
des Tliierreiclis ’ (1879 — 1893). 
3. Bresslan, E. — “ Beitrage znr Entwickelungsgeschiclite der Turhel- 
larien I,” ‘ Zeitsclir. f wiss. Zool.,’ 76 Bd. (1904). 
4. Goto, S. — “Studies on the ectoparasitic Trematodes of Jai^an,” 
‘ Journal College of Science, Imperial University of Japan,' 
vol, viii, i^art I (1894). 
5 . Graff, L. von. — “ Turhellaria.” Bronn's ‘ Thierreich,’ iv (1908). 
6. Hallez, P. — ‘ Embryogcnie des dendrocoeles d'eau douce,’ Paris 
(1887). ‘ 
7. “ Sur la nature syncytiale de I'intestin des Rhahdocoeles,” 
‘ Comptes Rendues,’ tome 146, pj). 1047-9 (1908). 
8. Haswell, W. A. — ‘ A Monograph of the Temnocephaleae,’ Macleay 
Memoiual Volume, Linnean Society of New South Wales (1893). 
9. “ Note on the Fauna of the Gill Cavities of Freshwater 
Crayfishes," ‘ Repoi’t Austral. Assoc. Adv. Sci.,’ vol. 8 (1901). 
' I have not been able to see this paper. What I have learnt regarding 
its contents has been obtained from Graff (5). 
