394 bulletin: museum of comparative zoology. 



the Mediterranean hydatina. The ribs are, of course, unequal, the 

 subgastric being very long, and extending over more than half the 

 length of the lappets. And the paddle-plates are very numerous. 



The course of the canals over the lappets is interesting, and was 

 easily traced. The upper, i. e. pharyngeal, loop is more easily under- 

 stood from the figure (Fig. A) than from a verbal description. It is 

 much less complex than in infundibulum. In the latter, according 

 to the descriptions of L. and of A. Agassiz the transverse trunk which 

 connects the loop on either side is bowed in the middle in a pro- 

 nounced double curve. But in the present specimen it is nearly 

 direct, there being merely a slight curve in the mid-line. The descend- 

 ing branches of its two lateral loops are thrown into a series of small 

 curves, but these vary in number on the two sides, and became more 

 or less pronounced according as the animal expanded or contracted. 

 In general the canals agree with those of Mayer's specimens. As 

 in the other species the inner surfaces of the lappets are provided with 

 a well-developed musculature of crossed fibres. 



The funnel-canal is very short, and the adradial canals empty 

 directly into the ends of the meridionals. The tentacular apparatus 

 is of the usual bolinid type. The specimen of 69 mm. is proportion- 

 ately broader than the one just described, and its lappets are longer, 

 extending beyond the mouth for a distance equal to two thirds the 

 polar length of the animal. That is to say, this specimen agrees very 

 well in its proportions with Mayer's figures. Furthermore the auricles 

 as in the latter, hung just beyond the mouth. When the animal con- 

 tracted transversely with the folding of the lappets, it became elon- 

 gated, and the stomach proportionately longer than when at rest. 

 The course of the canals was the same as in the larger example, except 

 for minor variations in the convolutions, which were less pronounced. 

 It is evident, then, that the external proportions differ considerably 

 at different stages in growth, or that they vary individually. 



Two young specimens of Bolinopsis were taken. In the younger, 

 10 mm. long, the lappets have just appeared, but are still very short. 

 In this respect the specimens agree with the young infundibulum 

 shown by A. Agassiz ('65). But in other respects they are much 

 further advanced, the ribs being longer, already with twelve paddle- 

 plates in each of the tentacular, sixteen or seventeen in the pharyngeal; 

 the stomach laterally flattened and of the adult triangular form, the 

 lappet-canals, both inner and outer, complete, and the tentacular 

 sheaths opening well below the level of the funnel, about mid-way 

 between it and the mouth-level. No trace of the auricles is yet to be 

 seen. 



