DORYMENIA PERONEOPSIS. 223 



immediately behind the external opening of the atrium, although otherwise 

 it is not especially modified externally. The ventral furrow is continuous with 

 the cloacal chamber. The cloacal opening is relatively large, ventrally placed 

 and is overarched by the posterior pointed end of the body, whose lateral mar- 

 gins may perhaps be separated in life to expose the genital spicula, the appear- 

 ance of the hinder end of the animal at such times resembling Ichthyomenia 

 ichthyodes. 



A well-developed dorso-terminal sense organ (Plate 7, fig. 7), visible in 

 sections only, is present about the level of the anterior margin of the cloacal 

 opening. It presents the usual cup-shaped appearance, is adjacent to the median 

 dorsal sinus entering the posterior end of the heart, and is innervated by two 

 nerves springing from the mid section of the suprarectal commissure lying 

 imiTiediately posterior to the pericardium. 



The cuticle investing the body is of more than average thickness (0.1 mm.) 

 and is developed by a hypodermal layer whose component cells are not clearly 

 defined and therefore are unfavorable for study. So far as could be determined 

 they comprise three types, columnar elements seemingly responsible for the 

 development of the cuticle, spicule-matrix cells which in early stages are indis- 

 tinguishable from the foregoing, and those forming the papillae. These last 

 named structures are stubby bodies (Plate 8, fig. 9), resembling an inverted 

 cone composed of highly vacuolated protoplasm in which nuclei are usually 

 visible throughout the entire organ. 



The spicules are hollow, needle-Uke bodies (Plate 8, fig. 2) those of alter- 

 nate layers crossing the others almost at right angles. In their formation no 

 points of especial interest have appeared. As usual several cells take part in 

 the process, and after functioning appear to shrink back into the hypodermal 

 layer without retaining any visible connection with the spicule. The average 

 length of fully developed spines from the sides of the body about the middle of 

 the animal measure from 0.4 to 0.48 nun. 



The anterior pedal gland is an organ of moderate size occupying the major 

 portion of the visceral caAdty between the level of the mid section of the atrial 

 cavity and the posterior border of the brain. The component pyriform cells, 

 measuring from 0.017 to 0.0216 mm. in greatest length, are early filled with a 

 stringy, vdolet colored secretion, after treatment with Delafield's haematoxylin, 

 which becomes finely granular in the later stages of its development. Each 

 cell is continuous, as usual, with a delicate ductule which opens by an inter- 

 cellular channel to the exterior. 



