WITH NOTES ON THE WEST INDIAN SPECIES. 



275 



The dermal pits of this species are so deep that they extend through more 

 than half the thickness of the body as shown in Text-figure 3. They lie in the 



Fig. 3. Transverse section throdgh genital region op Spengelia porosa showing dermal pits and pores. 



On the left of the figure a dermal pit is cut through the middle of its external orifice ; on the right 

 it is cut tangentially. 



cm. Circular muscles, d.l.m. Dorsal longitudinal muscles, d.p. Dermal pits. d.v. Dorsal vessel, l.g. Lateral 

 gonads (accessory genital ducts shown on the right), l.v. Lateral vessel, m.g. Medial gonads, v. Ventral 

 vessel, v.l.m. Ventro-lateral longitudinal muscles. 



submedian line, in direct continuation from the branchial groove on each side. They 

 are roughly but not exactly paired, no more than are the gill-clefts themselves. The 

 mouth of each pit is about 1 mm. in diameter. The most anterior pits invade the 

 posterior extremity of the branchial region, in consequence of which a number of the 

 outer pores of the posterior gill-slits do not open near the surface of the body, but 

 deep down at the base of the dermal pits. Apart from their connection with the 

 gut by means of the posterior gill-slits, the dermal joits do not communicate with 

 the intestine, although they extend very near to the wall of the latter. 



In the fresh condition the sides of the genital region were occupied by elongated, 

 somewhat pyriform bodies, which caused definite ridges on the external surface. These 

 projections were caused by the gonads. 



In the genital region accessory genital ducts occur both laterally and medially from 

 the dermal pits, so that several may be met with in a single transverse section. The 

 accessory pores of the lateral gonads do not perforate the longitudinal musculature, but 

 all occur within the interval, which is a very wide one, between the dorsal longitudinal 

 musculature, and the upper margin of the ventro-lateral longitudinal muscles (Text- 

 figure 3). 



The post-genital portion of the body was lacking from the single specimen which 

 was available for microscope examination. The individual was a mature male. 



