310 Z. ASCIDIOIDA. Cristatella. 



to the naturalist a spectacle of such singular curiosity and beauty 

 as perhaps can meet its supei'ior or rival in no other creature. I 

 am unwilling to borrow, from the memoirs of the foreign authors, 

 any additions to Sir J. G. Dalyell's short history, for I am aware of 

 the confusion to which such a practice has occasionally led, but no 

 harm can arise from the mention of some particulars which are evi- 

 dently generical. I may state then, that the tentacula are cihat- 

 ed like those of other ascidians ; the intestine has an oral and anal 

 aperture, the latter with a medial position ; and there is no trace of 

 any organ like what, in some other families of the order, has been 

 reckoned an ovary. The egg, according to M. Turpin, forms a small 

 flattened sphere with a papillous surface slightly incrusted with cal- 

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

 colour, the margin more transparent and yellowish, proving that the 

 egg is vesicular, — the exterior circle marking out the thickness of 

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

 the embryotic fluid. About 16 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 Httle 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 they are 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 

 lenticular, and entirely/ free of the spines which roughen them at a 

 later stage. Hence an easy solution of a question touching the man- 

 ner of escape from the mother, which, before this discovery, seemed 

 incapable of being eff"ected without a painful laceration from their 

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

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



* According to M. P. Gervais this is not the case, — the spines orignate sole- 

 ly from the line of junction between the marginal band and the disc ; — " du point 

 de contact de cet anneau et du corps disciforme partaient sur I'une des faces les 

 crochets doiit j'ai parle. Je reconnus depuis que I'autre face presentait aussi 

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



