266 LECTURE XIX. 



as being decomposed into almost imperceptible molecules, in which we 

 may recognise the ordinary result of the fissiparous property of its 

 constituent nucleated cells : their powers of assimilation are at the 

 same time manifested by the changes which they effect in the albumen, 

 at the expence of which they seem, in the first instance, to increase 

 their numbers and diffuse themselves over the surface of the vitellus. 

 This covering of the yolk Herold calls " coUiquamentum ;" he observes 

 that the original position of the germ-spot is indicated by a clear 

 transparent point (hyaline ?) ; that this point becomes thickened and 

 pearly ; then opake, so as to conceal the subjacent vitelline cells. A 

 similar change progressively extends over the coUiquamentum ; and 

 when one fourth of the circumference of the yolk is thus covered, the 

 opake layer has taken on a definite form, resembling the figure 8, the 

 smaller and anterior division being the base of the future head, the 

 posterior and larger one, of the thorax. A fissure is next observed to 

 divide the cephalic from the thoracic portion, the two parts being 

 distinct at this period, and determining the essential nature of the first 

 great segment of the body in the mature spider. The margins of the 

 thorax are next seen to be subdivided on each side by three parallel 

 fissures into four segments : these are the bases of the epimeral pieces 

 (^^. 115. 1, 2, S, 4.). The part of the opake integument which 

 connects the two series below is the rudimental 

 sternum. A second constriction begins to divide 

 the thorax from the abdomen; the mandibles or 

 antennae (b b) begin to bud forth as two con- 

 vex processes from the anterior part of the head : 

 the part intervening between these and the epi- 

 meral pieces forms the rudiment of the maxillee 

 (c). The intermediate labium also begins to be 

 defined from the sternum. The opake peripheral 

 layer (e), extending from the thorax to the op- 

 Embr>o bpider. positc end of the ovum, lays the foundation of 



the ventral integument of the abdomen. Upon the opake integument, 

 which is extending backwards over the dorsal part of the head, the 

 characteristic group of simple eyes (d) begins at this time to be dis- 

 tinctly developed, and the rudiments of the maxillary palps and of the 

 four pairs of thoracic legs become recognisable : now, also, the dorsal 

 vessel (/) appears along the upper curvature of the abdomen, and 

 thus all the chief characteristics of the future spider are manifested, 

 whilst the great mass of the vitellus remains still visible through the 

 transparent and incomplete lateral and dorsal parts of the integument. 

 The constriction between the two divisions of the body increases ; 

 the legs and palpi next present slight traces of articulations ; as they 



