THE BRITISH FOSSIL BRACHIOPODA. 



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slightly to the adjoining segment by the means of an organ of cylindrical shape. 

 Kowalevsky could not detect any traces of the nervous system. 



The muscular system of the larva is represented by delicate fibres, which pass from 

 the posterior portion of the intestine to the lateral walls of the thoracic segment. 



The mantle is composed of two layers, an external formed of pavement-epithelium ; 

 the other an internal consisting of small cylindrical cells. Between these two layers there 

 are very delicate muscular fibres. The edges of the mantle always carry on the ventral 

 side four bundles of bristles, which already existing in the preceding stages, have grown 

 and increased in length. 



At this stage the larva swims freely by the help of its vibratile cilia and by slight 

 movements of the head. At the approach of danger it vigorously contracts itself and 

 erects its bristles in all directions. All these movements recall those of the larvae of the 

 Annelida and in particular of those of the Mitraria. 



The larva after having swam for some time fixes itself; and then commences the 

 second stage of its development. 



Second Period. — The fixing of the larva to marine objects is effected by the means 

 of a sticky substance formed by the caudal segment ; as soon as fixed the larva begins 

 to turn up its mantle and to raise it above its head, so that in a little time the 

 mantle envelops the whole of the cephalic segment. On account of this folding 



Argiope {Cistella) Neapolitana, after Kowalevsky. 

 The larva after it has become fixed; s, bristles; y, eyes; m, muscles going 

 to the bases of the bristles; md, adductor muscles; mp, ventral peduncular muscles. 

 The thoracic segment is the part carrying the four bundles of bristles, ss, of which 

 two are median and two lateral. 



