158 DONDERSIA CALIFORNICA. 



develops branches, in reality openings, communicating with numerous lacunae 

 in the dorsal crest-like portion of the body. These in turn connect with others 

 of less extent in the lateral regions and through these with the pedal sinus. In 

 the head region the aorta breaks up into several sinuses which make their waj' 

 through the anterior pedal gland to connect with the pedal sinus and the more 

 lateral spaces just described. In the posterior end of the animal the blood 

 accumulates in large spaces surrounding the intestine and coelomoducts and 

 pours into the heart by means of a sinus passing dorsally on each side in the 

 neighborhood of the reno-pericardial openings. The pedal sinus continues 

 backward to the cloaca then pa.sses dorsallj' into a space beneath the shell gland 

 and from there into vessels leading to the heart. 



The gonad is distinctly paired, the two divisions being in contact only in 

 the middle of the body. Elsewhere they are widely separated by means of the 

 dorsal aorta. In the mid section spermatogonia are fairly numerous and at all 

 points ova arc commencing to develop. In the heart region the glands narrow 

 and communicate with the pericardium, which posteriorly communicates also 

 with the coelomoducts opening into the cloaca. The dorsal division of these 

 tubes is comparatively slender and is composed of cubical ciliated cells without 

 signs of glandular activity. No trace of a seminal receptacle is visible unless 

 what appears to be the anterior end of the ventral section may be so considered. 

 This lower division, or shell gland, is composed of rather low columnar cells, 

 tending to form longitudinal ridges, but they likewise are inactive. 



Beneath the single opening of the coelomoducts the cloacal wall is developed 

 into an outpouching which in the adult animal may develop copulatory spicula 

 or some gland connected with the egg-laying process, though in the present 

 specimen such functions are purely hypothetical. In shape this outgrowth 

 resembles a thick set Y, having a median undivided section which opens into 

 the cloaca and on the other hand connects with a blind pouch on each side of 

 the mid line. The walls are not unlike those of the shell gland, consisting of 

 columnar cells which are richly ciliated. 



The cloaca or mantle cavity in this specimen is of unusually small size 

 though it may increase in diameter as tlTe mature condition is approached. A 

 glance at Plate 6, fig. 2, will show that in this species the dorsal commissure 

 uniting the lateral nerve cords is placed uncommonly near the cloacal opening. 

 If in the adult the commissure is customarilj^ placed it might readily be 

 shifted by the active growth and enlargement of the cloaca. 



The nervous sj'stem is tj'pical. The brain is situated posterior to the atrial 



