34- The Field Naturalist's Quarterly November 



one of the chambers fuse into a mass, filling the whole chamber. They 

 then, by repeated subdivision, break up into a cluster of smaller cells, 

 ova or spermatozoa, according as the particular group is female or male. 

 In all animals the female reproductive cells are comparatively large 

 and few in number. The male cells, spermatozoa, are very small and 

 numerous. The essential act of fertilisation consists in a single sperma- 

 tozoon finding its way to an ovum, entering it, and becoming fused with 

 it. In order to accomplish this the spermatozoa have to be capable of 

 active locomotion. Each is therefore provided with a long whip-like 

 flagellum, by means of which it propels itself through the water. The 

 spermatozoa vary somewhat in shape, but only within narrow limits, so 

 that, whether they are those of the highest vertebrate or the lowest 

 ccelenterate, they more or less resemble in shape a tadpole with a small 

 body and a long tail. Only a very few spermatozoa succeed in finding 

 their way to an ovum, and this is evidently the reason that the male 

 cells so far outnumber the female, as otherwise few of the latter would 

 get fertilised. Nature is here profuse, but not wasteful. 



In Spongilla towards the end of the year there are produced in the 

 mass of the sponge a number of reproductive bodies called gemmules. 

 They are about the size and shape of mustard seeds, and are of a very 

 curious structure, having spherical flinty skeletons made up of spicules 

 shaped like two wheels connected by an axle. Soon after these gem- 

 mules are produced the whole sponge dies, leaving them embedded 

 within the dead skeleton, which gradually breaks up and liberates 

 them. They lie dormant through the winter, but develop into fresh 

 sponge colonies in the following year. The production of these gem- 

 mules seems to be peculiar to the freshwater sponges, whose conditions 

 of life demand the winter " rest." Marine sponges have no such need, 

 being functionally active from year's end to year's end. 



Suburban Bird Life. 



By R. W. Heenan. 

 Notes recorded within a few miles radius of Twickenham. 



Missel-Thrush 



Song-Thrush . 



Fieldfare . . 



Redwing . . 

 Blackbird . . 

 Wheatear . . 



Winchat . . 

 Redstart 



Not uncommon at any time, and occurring in 

 flocks in autumn. 



Common everywhere. Heard one singing at 

 2.55 a.m. on 22nd June. 



I have seen them near Hounslow and in Rich- 

 mond Park in winter. 



Frequents the. fields in winter in scattered flocks. 



Common. 



Many in Richmond Park, where I saw one sing- 

 ing on the wing. 



Richmond Park. 



Not uncommon in summer. 



