260 MORPHOLOGY OF INVERTEBRATE TYPES 



endostyle, but the ventral pair is much more curved than the 

 dorsal pair. The ridges are perforated by openings called stig- 

 mata. The stigmata establish a direct communication between 

 the pharynx and the cloacal chamber by way of the peripharyn- 

 geal (or peribranchial) cavity into which they open. There is 

 also a ciliated mbratile tubercle, or better, ridge, in shape an in- 

 complete oval with involuted ends, situated between the peri- 

 pharyngeal groove and the tentacle sieve above the starting 

 point of the dorsal lamina. It surrounds the opening of the ad- 

 neural gland. As will be shown later, the pharynx is rich in 

 blood-sinuses. As water is drawn into the pharynx through the 

 incurrent siphon, the food particles pass into the oesophagus, 

 driven thither by the action of the endostyle, while the water 

 enters the peribranchial cavity through the stigmata and is again 

 expelled through the cloacal siphon. The opening from the 

 pharynx into the oesophagus is a small oval. It is situated at 

 the lower extremity of the dorsal lamina. The (esophagus is 

 quite short and is considerably constricted at the place where it 

 opens into the stomach. A digestive gland composed of several 

 tubular lobes and known under the name of liver opens into 

 the stomach near its cardiac end. The stomach is a curved, 

 U-shaped tube of considerable diameter. It runs first down- 

 ward and forward and then upward. Here the canal changes its 

 course and structure. It becomes the intestine and runs in an 

 opposite direction to the stomach, dorsal to it, first downward 

 and backward, then upward. The anus opens into the cloacal 

 chamber in the mid-dorsal line. 



Excretory system. Molgula has no excretory organs com- 

 parable to those of other invertebrates. Waste products are 

 stored in a bean-shaped kidney which is situated on the right 

 side of the animal and is devoid of any duct or opening. There is 

 another organ of unknown function which is supposed to be an 

 organ of excretion. This is the adneural gland, 1 situated dorsal to 

 the nervous ganglion between the two siphons. The duct of the 

 1 Usually called subneural. 



