The anatomy of a pteropod, Corolla (Cymbuliopsis) spectabilis Dall. 69 



sets of muscle fibres whose general appearance and position are re- 

 presented in Figs. 1 and 2. 



As is shown in Fig. 7 the mantle of this species arises from 

 the dorsal side of the visceral mass at its junction with the fin. 

 Curving ventrally it encircles the visceral nucleus and terminates in 

 a free edge about the middle of the foot. Within its tissue the trans- 

 parent casque is developed. Immediately in front of the visceral mass 

 the mantle cavity narrows to a small circular opening symmetrically 

 placed in the mid line. Between the free edge of the shell and the 

 opening into the mantle cavity proper the epithelium is modified to 

 form the palliai gland whose histological characters are almost identical 

 with those of C. calceola as described by Peck^). 



Another feature present in other members of the genus is a dark 

 brown pigmented cap developed in the superficial tissue of the visceral 

 mass at its posterior extremity. In some specimens this is uniformly 

 rounded and is closely applied to the visceral mass. In numbers of 

 other examples it becomes, as Pelseneer states, sucker-shaped in 

 form and in our specimens the substance composing it appears in 

 such cases to be larger in amount. No relation has been traced 

 between its size and the maturity of the sex products. 



The Digestiye System. 



The general position of the organs of the digestive tract has al- 

 ready been described. Its first division, the funnel-shaped mouth, is 

 provided with dehcate sensitfve lips whose cilia serve to collect the 

 food products consisting chiefly of diatoms, quantities of organic debris 

 and an occasional copepod. Such a diet demands no buccal armature 

 and none is present. Salivary glands are also wanting. Continuing 

 backward the buccal cavity passes into that of the oesophagus whose 

 epithelial lining is thrown into numerous secreting folds. Separating 

 these cells from the thin external sheath of circular and longitudinal 

 muscles is a scant layer of connective tissue cells imbedded in a 

 gelatinous matrix. 



In the stomach the lining epithelium is modified into five patches 

 each of which secretes a tooth. Of the latter four are relatively very 

 large (Fig. 12) while the fifth, as in others members of the genus is 

 minute and is located in the forward end of the dorsal side of the 



1) On the anatomy and histology of Cymbuliopsis calceola, in: 

 Stud. biol. Lab. Johns Hopkins Univ., V. 4. 



