ANATOMY OP ACLESIA FREERI. 



71 



mens. The parapodia are traversed by numerous muscle strands 

 passing from the outer to the inner wall. An irregular network 

 of larger muscle bands lies next to the internal surface, which 

 can be clearly seen when the parapodia are reflected. Outside 

 of the horizontal muscle layer, but close to the internal surface 

 of the parapodium, is a network of venous sinuses which forms a 

 quite definite layer (fig. 8, Plate II). 



There being no trace of a shell, the mantle is reduced to a 

 ridge which passes from near the anterior side of the branchial 

 cavity around the left end of the gill, finally ending behind the 

 gill near the base of the anal 

 papilla. The pericardium and 

 nephridium lie to the left of the 

 ridge, raised somewhat above 

 the general level of the floor of 

 the branchial chamber. The 

 highest part of the mantle ves- 

 tige, near the posterior end, 

 projects from 5 to 7 millimeters, 

 sufficient to enable it to overlie 

 a few small plates of the pos- 

 terior end of the branchia. The 

 anterior end of the mantle ridge 

 is brillant black, and is com- 

 posed of denser tissue than the 

 reman der of the ridge. The 

 posterior extremity of the man- 

 tle ridge is also pigmented. 



These aclesias have the power, 

 possessed by most tectibranchs, 

 of emitting a purple dye when 

 they are greatly disturbed by 

 handling, or when the water in which they are kept becomes un- 

 bearably stale. 



The dye is emitted by this species in smaller quantity and with 

 more reluctance than by any other aplysiid with which I am 

 familiar. The great majority of the specimens which have been 

 killed, either by asphyxiation or by narcotization, have died 

 without giving forth any trace of dye. 



The dye is produced from the pigmented areas at the anterior 

 and posterior ends of the mantle ridge, the anterior region pro- 

 ducing the greater amount. The pigmented areas of the mantle 

 ridge can be squeezed in a moribund aclesia, when the purple dye 



Fig. 1. — Diagram of the pallial complex of 

 Aclesia freeri sp. nov. : a, anal papilla ; 

 bv, afferent branchial vein ; Tnr^ mantle 

 ridge, i. e., the projecting free margin of 

 the reduced mantle ; n, nephridium ; o. 

 osphradium ; par, parapodium ; p. c, 

 pericardium ; v, vein of left side of body 

 running beneath the pericardium and 

 nephridium ; vu, vulva ; x, aperture by 

 ■which the blood from the hasmocoal and 

 veins of the right side of the body enters 

 the branchial vein. 



