390 POLYZOA HYPPOCREPIA. 



ovarj. The egg, according to M. Turpin, forms a small flattened 

 sphere, with a papillous surface slightly incrusted with calcareous 

 matter. The centre is of a dark reddish-brown or vinous colourj 

 the margin more transparent and yellowish, proving that the egg is 

 vesicular, — the exterior circle marking out the thickness of the co- 

 coon or shell, and the more opake disk the part occupied with the 

 embryotic fluid. About sixteen rough spines radiate stiffly from the 

 circumference : they are tubular, yellow, terminated with from two 

 to four crotchets, and apparently vary in length, for they arise 

 alternately from the edge and from the surface a little behind this.* 

 The egg is filled with an albuminous granular fluid analogous to the 

 vitellus or yolk, for in it the foetus is perfected after a period which 

 probably depends, in a great measure, on the temperature of the sea- 

 son in which the egg is laid. The time of birth having arrived, the 

 shell opens in two gaping halves, as an oyster opens its valves, to 

 permit the escape of the young polypus, which enters on its existence 

 complete in all respects, either a single individual, or with one or 

 two others, less mature, pullulating from the sides. 



One of the most interesting facts ascertained by M. Turpin is that 

 the eggs before exclusion, and immediately after, are oval or len- 

 ticular, and entirely free of the spines which roughen them at a later 

 stage.f Hence an easy solution of a question touching the manner 

 of the egg's escape from the mother, which, before this discovery, 

 seemed incapable of being effected without a painful laceration from 

 its bristling armature. This alteration in the structure of the egg 

 is very remarkable, although not singular, for the eggs of several 

 mites are known to undergo somewhat similar changes. The eggs 

 float in the water from their lesser specific gravity, but often they be- 

 come attached by their spines to the filaments of conferviB, &c., where 

 they float until the young are hatched, and where these find an im- 

 mediate place of rest. 



M. Turpin has stated that some varieties of silex contain immense 

 numbers of the ova of the Cristatella and Alcyonella, preserved in 



* According to M. P. Gervais this is not the case, — the spines originate solely 

 from the line of junction between the marginal band and the disk : — " du point de 

 contact de cet anneau et du corps disciforme partaient sur Tune des faces les crochets 

 dont j'ai parl^. Je reconnus depuis que I'autre face presentait aussi les appendices en 

 crochets, mais qu'ils y etaient moins allonges." 



t " The ova in their j'oung state are inclosed in a ciliated membrane, and the 

 hooked spines with which, in their more mature condition, they are furnished, are 

 developed within the ciliated investment, being yet fully formed previously to the ova 

 quitting the parent." Pro/. Allinan. 



