194 BULLETIN OF THE 



passes to the dorsal flexure from the internal end of the oesophagus, is fully 

 formed before any trace of the anal ring of cilia or the lateral bodies (" lap- 

 pets ") found near the stomach have appeared. 



The second of the two figures of Tornaria (Fig. 17) is taken from a larva 

 still older than the last, from which it differs in one or two particulars. The 

 most important character which has been acquired in the growth of the former 

 is a belt of cilia not far removed from the anal pole, which is found in all later 

 stages in the development of the worm up to its metamorphosis into Balauo- 

 glossus. The same ciliated belt we also find in the larva P. recurvatum, the 

 young of the Nemertean worm which we have studied, but it does not exist 

 in the known species of Pilidium, which are the nearest allies of our new 

 Nemertean larva. It is, however, represented in Actinotrocha. 



A noticeable fact is that the lateral bodies found near the stomach in older 

 Tornarioi have also not yet appeared in the growth of the internal organs at 

 this stage of development. 



There is another difference between the second and the first of these two 

 larval youngest stages of Tornaria. On either side of the oesophagus, originat- 

 ing from the inner end of the muscular thread which arises from the eye-spots 

 at the apex of the larva, is found a pair of rein-like bodies in the form of 

 threads, which exteiid to points on either side of the mouth. It is not known 

 what their function is, but their position is the same as that of like threads 

 which have been described elsewhere in this paper, for the first time, in our 

 common Loven's larva, similar to its European representative, referred by 

 Schneider and Hatschek to the strange genus Fohjgordius. There is also an- 

 other characteristic in the A'ery young Loven's larva never yet observed by 

 others, which seems to me of some importance in theoretical questions con- 

 cerning the affinities of Polygordius. A very young Loven's larva was found, in 

 which a long vibratile cilium is borne upon the apex, just as has been mentioned 

 in Pilidium and' the larva of the above-described Nemertean. Moreover, this 

 cilium, which has the character of a flagellum as far as size goes, rises from a 

 specialized portion of the body of the larva upon whicli eye-spots are borne. 

 The flagellum in Loven's larva is an embryonic structure, and the portion of 

 the larva which carries it is directly changed into the head of the future worm. 

 In the Nenierteans, however, the flagellum is embryonic, like that of Loven's 

 larva, but the body of the larva plays no part in the formation of the head of 

 the worm, but by its wonderful metamorphosis makes the whole posterior 

 extremity of the larva. No Tornaria has been observed with this flagellum 

 at its apex, unless we homologize with it a small tuft of cilia larger than 

 the others on the surface of the body, found at the apex of our youngest larva. 

 Close as the resemblances between Tornaria and Pilidium recurvatum are, 

 there are many very intimate relationships between the latter and the young 

 of the Gephyrean worm Phoronis when known as Actinotrocha. The rapidity 

 of the transformation of the Pilidiuvi into the Nemertean, more especially the 

 apparent evisceration and turning inside out of the larva at that time, led me 

 at first to regard my larva as the young of some unknown worm allied to 



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