ARACHNIDA. 



213 



o J5 



a 



ance, through which, however, the globules 

 of the vitellus may be distinguished. A single 

 point remains perfectly transparent, and this is 

 observed at the extremity of the egg (Jig. 107, 

 ,) opposite to that which the germ occupied 



Fig. 107. a ^ ter i ts displacement. 



Heroldtcalls this clouded 

 alb\imencolliquamenttim. 

 Up to this period the 

 vitellus seems not to un- 

 dergo any change ; all 

 that has been hitherto 

 observed takes place in 

 the albumen and in the 

 circular space between 

 the yolk and the shell. 



Sixth period. The colliquamentum, or 

 clouded albumen, which was extended over 

 the yolk so as to conceal it, is now concen- 

 trated upon the point last occupied by the 

 nucleus of the germ, and has assumed a pearly 

 colour (Jig. 108). Its consistence is pretty 

 Fig. 108. solid ; it is opake, so that 



the globules of the yolk 

 can no longer be distin- 

 guished through it, al- 

 .6 though they are elsewhere 

 more conspicuous on ac- 

 count of the retreat of the 

 clouded albumen towards 

 this single point; from 

 this moment the colliqua- 

 mentum, which seems to have changed its 

 nature, receives a new name, and is designated 

 by Heroldt the cambium. The cambium covers 

 more than a fourth part of the circumference of 

 the yolk; its form is already pretty well marked, 

 and two parts may be distinguished in it; 

 one large (6), the other small (</), which are 

 separated by a kind of contraction. The form 

 of the larger division is elliptical, and it is in 

 its substance that the thorax, the legs, and the 

 essential internal parts of the foetus will soon be 

 perceived to develope themselves. The smaller 

 division is of a rounded form, and seems, as it 

 were, an appendage to the preceding; it is 

 destined to give origin to the head, the or- 

 gans of sense, and the appendages of those of 

 mastication. So much being premised, we 

 may call, with Heroldt, the larger division 

 cambium thoracicum, the lesser one cambium 

 cephalic-urn. We may also, for the better 

 comprehension of the changes which are about 

 to succeed each other, divide the superficies 

 of the ovum into four regions. That which 

 contains the cambium may be called the pectoral 

 region, the opposite portion may be called the 

 dorsal, and the two intermediate parts the 

 lateral regions. We may observe that in other 

 species of araneae where the ova are spherical, 

 the germ is at once converted into colliqua- 

 mentum, and then into cambium, without a 

 change of situation. The Aranea diadema offers 

 an example of this circumstance ; in other re- 

 spects there is no important difference observable. 

 Seventh period. The two portions of the 

 cambium, the cephalic and thoracic, have 

 as yet presented only the appearance of an 



Fig. 109. 



a 6 



opake and 



homogeneous 



mass, but now we 



may distinguish traces of rings, four in number 

 on either side ; these are the rudiments of the 

 legs. (Fig. 109, 1, 2, 3, 4.) They occupy the 



lateral aspects of the 

 anterior part of the 

 ovum ; they are also 

 visible on the pectoral 

 region, towards which 

 they are prolonged in- 

 feriorly. The extre- 

 mity of the first leg is 

 contiguous to that of 

 the opposite side ; but 

 the three others, though 

 of greater length, yet 

 do not reach so low down, but leave a triangular 

 interspace between them, which is filled with 

 a cloudy and somewhat transparent matter, 

 through which the vitelline globules are visible. 

 This triangular space, which is subsequently 

 to be covered by the legs, seems to give origin 

 to the trunk and to many parts contained in 

 the abdomen. In tracing the two portions 

 of the cambium through the changes which 

 they have undergone, we find that the thoracic 

 portion is represented by the legs and their 

 intermediate space, and that the cephalic por- 

 tion is anterior to this. The alterations of the 

 latter part are not less remarkable ; instead 

 of being rounded anteriorly it is truncated, and 

 we may perceive a ring at the sides, which is not 

 divided on the inferior middle line of the body, 

 and which represents the maxillary palps (/>). 

 One may even distinguish, as if through a 

 cloud, the rudiments of the mandibles. It 

 is probable that all the parts which appertain 

 to the head, as the eyes, the mandibular 

 hooks, and the maxillae, have their limits well 

 defined from this period. With respect to the 

 head, (a) it is neatly separated from the chest ; 

 and this fact it is of importance to dwell on, 

 since in all the full-grown spiders the conflu- 

 ence of the two parts is most intimate, and their 

 original separation only indicated by a groove 

 of greater or less depth. The ovum, also, 

 now presents some other new appearances; 

 these are a kind of furrows or arched folds 

 (c c), which are seen on the vitellus behind 

 the legs ; and which deserve attention, since 

 they indicate the formation of the common 

 teguments of the foetus. And we must here 

 observe that the parts which are already de- 

 veloped have an intimate connection with the 

 vitellus. Thus if an ovum be opened with 

 all the precautions requisite for so delicate an 

 operation, and if the matter of it be extended on 

 a piece of glass, we see that the parts formed 

 in the cambium preserve their general figure, 

 and that the internal layer of the mucous and 

 whitish matter of which it consists is in intimate 

 communication with the vitellus. It is implanted 

 upon the yolk just as fungi and other parasitic 

 plants are attached to the trunk of a tree : the 

 yolk, then, is subservient to the nutrition of 

 the most exterior parts of the body. 



Eighth period. The exterior parts which are 

 developed in the cambium, viz. the feet, the 

 mandibles, and the head, are more neatly de- 

 fined. The ovum (fg. 110) now presents a 



