TEREBELLA. 207 
to receive the head. None of any other form has been seen. This 
sheath is frequently abandoned and as often resumed ; neither does the 
animal restrict itself to the construction of one sheath only. 
A peculiar feature in its history is producing a real cobweb, as dis- 
tinct as that of the spider, with which it covers itself, and which also fre- 
quently, if not always, serves to support its spawn. The texture is very 
thin, rather irregular, and composed of the finest threads, these almost invi- 
sible, from their slenderness and extreme transparence. Neither the mode 
of formation or extension, nor the expedients for securing their extre- 
mities are obvious. 
Such a web, from the specimen nine lines long, covered an area 
fifteen lines square. This is plainly a work of some exertion, as the 
' threads, sometimes amounting to fifty, are fixed to the side of the vessel, 
as high above the bottom as equals the length of the weaver, or more, 
and they also extend below, there to be secured. Thus it is evidently 
an artificial work, and it receives successive accessions. The specimen 
continued its work about three weeks in May, but although surviving a 
month longer, it wove no more. 
Such a web has been formed by four different specimens, and always 
in May. These alone came under special observation. 
During the first week of this month a cluster, consisting of thirty- 
seven white elliptical ova, as I concluded then, was removed in succes- 
sive portions by a small specimen contained in the same vessel, which 
had meantime spread an irregular cobweb. These were not its own ova, 
but the product of some other animal, nor were they sustained by a 
web. 
The spawn of this species is of a different character. Seven years 
after the preceding incident, just about the same season, a specimen, 
quite an inch long, produced above 1000 spherical carmine ova in the 
course of two days ; and perishing accidentally a fortnight later, many 
more escaped on rupture of the body. At the same time another speci- 
men proved very prolific. 
The spawn consists of irregular albuminous matter, of various quan- 
