1(;0 ICHTHYOMENIA POROSA. 



thickened edges especially on tlie rounded extremity. Scattered fairly regu- 

 larly among the first variety are those of the second type, paddle shaped, with 

 short handle and a length of 0.054 mm. Along the ventral furrow they are of a 

 greater length, 0.01 mm. 



The hypodermis is a])parently one cell thick but the species is peculiar in 

 iiaviiig the layer d('Vclo])ed into many transverse folds (Plate 32, fig. 7) especially 

 on th(> dorsal surface, and in section these ridge-like elevations render the cell 

 relations ol)scure. These wrinkles are more pronounced in some specimens 

 than in others, and are usually more prominent in the anterior half of the body. 

 In some cases they are doubtless due to reagents but usually they are certainly 

 normal. The ordinary type of hypodermal cell is very slender, especially in the 

 ridges and is provided with a relatively dense subcentrally placed nucleus. 

 Accompanying these are numerous larger, more globular cells, apparently in 

 large measure empty in preserved material. This may be due to the precipita- 

 tion of some highly watery secretion, oi- more probably to the decalcification of 

 some calcareous jiroduct. 



This species possesses upwards of fifty remarkable organs, apparently 

 sensory, located chiefly about the anterior end of the body in front of the outlet 

 of the anterior pedal gland. All are situated in the ventral half of the animal. 

 Each consists of an invagination of the hypodermis (Plate 24, fig. 12) with an 

 average depth of 0.1 mm. The lining cells are low, very indistinct and are 

 pro\i<led with what appear to be very long cilia, which in most cases extend 

 slightly beyond the general body surface. In the most favorable specimens 

 delicate fibres attach to some of the cells Init on the other hand they have never 

 l)e(Mi traced to any undoubted nerve. It is impossible to determine their func- 

 tion yet it may l)e that in life they act as tactile organs like the apical tuft in 

 the trochophore larva. 



The anterior pedal gland is comjiaratively large (Plate 24, fig. 1) and occu- 

 pies much of the visceral cavity between the ati'iuni and the forward boundary 

 of (he stomach-intestine. Its cells are arranged in large groups and are filled 

 wi(h a uniformly graiuilar, lightly staining secretion that after its escape appears 

 as a viscous, darkly staining substance. The posterior jiedal gland consists 

 of c(>lls filled with a darkly staining, finely granular secretion clearly distinguished 

 from (hat of the foregoing group. Anteriorly it rests against, and opens through, 

 the posterior wall of the outlet of the anterior pedal gland, and more posteriorly 

 forms a thin sheet resting against the ventral body wall and opening between 

 five folds in the ventral furrow. Posteriorly these folds very soon disappear 

 save one, the foot, and the accompanying glands diminish greatly. 



