Post- Larval Stages of Arenicola 77 



vincenti, he concluded, chiefly because of differences in the structure 

 of the chaetae, that the two forms did not stand in this relationship. 

 He believed the genus Clymenides (with three species) to be homo- 

 geneous, defined it, and regarded it as intermediate between the 

 Clynienidae (Maldanidae) and Arenicolidae. While admitting that 

 he had not seen gonads in any specimen, he expressed the opinion 

 that, if these examples of Clymenides had an ulterior development, 

 it would not be towards Arenicola but parallel to it. His studies 

 on these worms led him to put forward the view that there is a 

 continuous series connecting the Maldanidae and Arenicolidae, and 

 to suggest the union of these two families (see p. 27). 



Prof. Fauvel's 1 investigations led him to the conclusion that 

 C. sulphur eus was the young of Arenicola marina, that C. ecaudatus 

 and C. incertus were stages in the growth of A. ecaudata, and that, 

 therefore, the genus Clymenides was invalid. By keeping an example 

 of C. ecaudatus in an aquarium until it grew into an A. ecaudata 

 50 mm. long, he produced conclusive proof of the identity of these 

 two forms. 



In a paper published in the same year Prof. Mesnil 2 admitted 

 that C. sulfur eus and C. ecaudatus were early phases of A. marina 

 and A. ecaudata respectively, and expressed the opinion, based on 

 renewed observations, that C. incertus was probably the young 

 form of Branchiomaldane vincenti. The writer is able to confirm this 

 opinion after having examined, through the courtesy of Prof. Mesnil, 

 the three original specimens of C. incertus. 



Thus the species of Clymenides have been merged either with 

 Arenicola or with Branchiomaldane, and Clymenides therefore dis- 

 appears as a generic name. 



Post-Larval Stages of ARENICOLA MARINA. 



The earliest known stages of Arenicola marina have the full 

 number of chaetiferous segments and about twenty tail-segments. 

 They are found in the surface waters of the sea, not far from shore, 

 each enclosed in a mucous or gelatinous tube, which usually extends 

 beyond the worm at either end (PI. X, Fig. 26). The worm is capable of 

 wriggling movements, which are but little impeded by the enveloping 

 tube. Nothing is known concerning the duration of the pelagic life 

 of the post-larval stage, but it is apparently at least several days. 



1 C. E. Acad. Sci. Paris, cxxvii (1898), p. 733; Proc. 4th Int. Congr. Zool. 

 (1899), p. 229. 



2 Zool. Anz., xxi (1898), p. 637. 



