324 Mr. A. Tulk on the Anatomy of Phalangium Opilio. 



the exit of tlie seminal secretion, is turned from instead of towards 

 tlie female, and from its mode of articulation witli the body of 

 the penis, cannot be bent in the opposite direction, a mechanical 

 difficulty is suggested which serves to support the account given 

 by Latreille. More detailed and careful observations are much 

 needed upon this subject, as should the generative function be 

 performed in the manner described above, without true intromis- 

 sion, what then can be the use of the well-developed condition of 

 the male organ ? 



Nervous System. — In the conditions of their nervous system 

 the Phalangia conform very closely to the type of structure exhi- 

 bited by the Anourous Arachnida. Owing to the relative posi- 

 tion of their oral organs, which, from the absence of a distinct 

 head, are removed inferiorly upon a level with the coxae of the 

 legs, of which indeed they are but modifications, the anterior or 

 cephalic (Pl.V. fig. 31. eg) mass is placed m. front instead of above 

 the oesophagus, the latter bending obliquely downwards, after 

 crossing the thoracic ganglion, to reach the above structures. It 

 consists of two oblong and obtusely conical ganglia of a grayish 

 white colour, the apices of which are directed forwards, their bases 

 prolonged into two short crura which connect them to the sides 

 of the anterior margin of the thoracic ganglion, and leave an el- 

 liptical opening (*) through which the oesophagus passes. They 

 are invested together by a loose neurilemma, and give ofi' at least 

 three distinct nerves. The middle one, of large size, arises by a 

 common origin, somewhat dilated, and divides about its middle 

 into two trunks (o/i), which pass upwards between the anterior 

 caeca of the alimentary canal, the muscles of the chelicerse and 

 maxillary palpi, to expand upon the inferior surface of the central 

 conjoined pair of eyes. The two others {lo) are much smaller, and 

 are directed outwards to the lateral eyes. 



Conditionated by the amount of nervous energy required for 

 setting in motion the long and filiform extremities and sustaining 

 upon them the weight of the body, the thoracic ganglion [tg) is 

 of great extent, occupying nearly the whole lower surface of the 

 cephalo-thoracic cavity. It is of a paler colour and firmer tex- 

 ture than the cephalic, apparently made up by the union of two 

 or more ganglia, and consists of a transverse portion lying behind 

 the oesophagus, the anterior and posterior margins of which are 

 elliptical and well-defined, and of two lateral prolongations ex- 

 tending forwards and backwards upon either side of the above. 

 Anteriorly these reach as far as the extremities of the cephalic 

 gangha, curve slightly downwards, and give ofi* a nerve from their 

 apex and one also from their internal margin, while behind they 

 are very short and obtuse, and furnish each a large trunk to the 

 posterior pair of legs, three others [en) being distributed from 



