any other change two gills develop from the round bag-shaped di- 

 verticula of the oesophagus, and afterwards three more pairs of gill- 

 slits arise, somewhat as in the } T oung Ascidian. Agassiz then re- 

 marks that the "passage of Tornaria with the young Balano- 

 glossus is very sudden, taking place in a few hours; but unlike 

 the transition from the Pluteus into the Echinoderm, there is no 

 resorbition of any portion of the larva." The body lengthens, 

 the proboscis is indicated and assumes much of the form of 

 the adult, the four pairs of gills are well developed, the cilia drop 

 off first, the longitudinal bands and finally the transverse ones, 

 and then the collar becomes well marked. The young worm, for 

 it rapidly assumes the adult Balanoglossus likeness, though much 

 shorter proportionally, now instead of swimming " creeps rapidly 

 over the bottom by means of its proboscis, which acts as a sort of 

 propeller taking in water at the minute opening of the anterior 

 extremity of the proboscis, and expelling it through an opening 

 on its ventral side immediately in front of the mouth:" 



Fig. 221, after Agassiz, represents the youngest stage found in 

 the sand, but it differs from the adult simply in the shorter body 

 and less distinct development of the collar, with fewer gills and 



There is considerable difference of opinion regarding the affini- 

 ties of this worm. On first digging it out of the sand at Beaufort, 

 N. C, it seemed to us a most anomalous form, the large soft pro- 

 boscis, the singular gills, and the absence of setiform feet, appa- 

 rently forbidding its relationship to the true Annelides. Yet its 

 true position appears to be between the leeches and setiferous An- 

 nelides, with some Nemertian analogies. The reader can choose 

 between the opinion of Gege I lr tl it tl worm is the type of 

 an order equivalent to the Annelides, or a true Annelid allied to the 

 Terebrellidje, Clymenidaj and allied Annelides, as suggested by 

 Metschnikoff and Kowalevsky ; or that of A. Agassiz who regards 

 it as the type of a family intermediate between tubicolous Annel- 

 ides and Nemertians." 



Turning now to the lowest Annulata, the leeches, in which there 

 are no bristles or gills, while each end of the body terminates in a 

 sucker, it has been found by Rathke ami Kowalevsky that their 



which there are bristles. In the leeches the sexes are united in 

 the same individual, except in the genus Malacobdella. The eggs 



