GENERAL FEATURES, METHODS, ETC. 21 



attached near the radula. A (lefinite digestive gland is wanting, the mid-gut 

 pouches being lined with hepatic cells. 



Owing to the great reduction of the foot and correlated changes, several 

 peculiarities appear in connection with the circulatory system. As in the 

 Chitons the heart is posterior, and the aorta passes along the mid line dorsal 

 to the gonad to connect with the head cavity, which in Limifossor is limited 

 posteriorly by a weii-d('\eloped septum. In this genus there are indications also 

 of a pedal sinus, but l)eliind the lunxd region it largely disappears, the Ijlood 

 flowing between the gut and body wall to the branchial region. Passing through 

 the ctenidia, or the folds in the cloacal wall, when these are jiresent, the blood 

 makes its way to the posterior end of the heart. 



The nervous system bears a striking resemblance to that of the Chitons. 

 There is a greater concentration of the nerve cells to form well-differentiated 

 ganglia, but otherwise there are, in such species as Proneomenia hawaiicnsis, no. 

 especially unique features. The supraoesojihageal mass originates three pairs 

 of nerves, which innervate the buccal and ncMghboring body walls and three 

 pairs of coimectives, the laltiobuccal, pedal, and lateral. The first named, in 

 a ty]Mcai condition, is decidedly Chiton-Hke both as regards its position and 

 elements. The otlier two, passing backward throughout the entire length of 

 the animal, are united fnM[uently by connnissures and connectives, and may 

 fuse completely (Chaetodermatidae) in the cloacal region. In a mnnl)er of 

 other species the pedal cords, after diminishing in size in the hinder regions of 

 the body, may lack any connection with the lateral ganglia, or they may termi- 

 nate in ganglionic enlargements (gdiujlion po.sterius infcrius of Wiren) united 

 by connectives with similar swellings {gaii(/. pust. supcrius) on the end of the 

 lateral cords. The latter ganglia are invarialjjy united by a heavy connnissure 

 passing dorsal to the rectum, antl the pedal cords likewise may be comiected 

 by a subrectal commissure, thus completing a cinaunrectal Jierve ring. 



In the .Solenogastres the secondary body cavity comprises that of the 

 gonad, pericardium, and the ducts leading from this latter space to the cloaca. 

 In the Neomeniina the species are herifi!^fl^BPig|^tic ; in the Chaetodermatina 

 dioecious. The sexual elements pass through the pericardial cavity into the 

 coelomoducts, whicli in an immature condition are relatively simple, and in 

 some species at least are not fused before they open into the cloacal cavity, 

 characters which the Chaetodermatina retain throughout life. In the Neo- 

 meniina, on the other hand, \arious modifications may occur which produce a 

 high degree of complexity. Two or more seminal receptacles are usually present, 



