GENERAL CONSIDERATIONS. 83 



is said often to be unattached and sunk into a sand-tube, so that in 

 respect to this habit there is a marked similarity to Plioronis. 



It should here be mentioned that a few zoologists have assumed a 

 near relationship to exist between the Chaetognatha and the Brachio- 

 poda, chief among these is van Bemmelen (No. 2), and the view has 

 also been advocated by Butschli,* 0. and R. Hertwig (coelom- 

 theory). These assumptions are based upon the agreement in the 

 first stages of development, the rise of the coelom by folding, the 

 development of three body-segments, and on those anatomical 

 features common in the two groups as a consequence of the similar 

 orioiii and nature of the enterocoele. The adult forms difller 

 altogether in manner of life, and show essential diflerences of 

 structure, the cephalic section especially being developed in an 

 altogether different way in the two groups. Further, the Brachiopoda, 

 in consequence of the agreement of the larva with tlie AdinotrocJia, 

 seem to be allied to the Trochophore type, Avhile no such affinity has 

 as yet been propounded for the Chaetognatha. The estaljlishment of 

 relationships between these two groups seems therefore to be still 

 very doubtful, and their structural resemblances appear to be mere 

 analogies. In any case it would only be possible to admit some very 

 remote connection between the two, 



LITERATURE. 

 1 Beeoher, C. E. Development of the Brachiopoda. American 

 Journal of Science. Part I., Vol. xli., 1891. Part II., Vol. 

 xliv., 1892. 



2. Van Bemmelen, J. F. Untersuchungen liber den anatomischen 



und histologischen Bau der Brachiopoda Testicardines. Jen. 

 Zeitschr. f. Naturw. Bd. xvi. 1883. 



3. Blochmann, F. A^orlaufige Mittheilung liber Brachiopoden. 



Zool. Anz. Jg. viii. 1885. 



4. Blochmann, F. Ueber die Anatomic und die verwandtschaft- 



lichen Beziehungen der Brachiopoden. Archiv. des Vereins 

 der Freunde der Naturgesch. in Mecklenburg. Jg. xlvi. 1892. 

 Cf. also Blochmann, F., Untersuchungen liber den Bau der 

 Brachiopoden. Jena. 1892. 



5. Brooks, W. K. Development of Lingula. Chesapeake zoolog. 



Laboratory, Scientif. ResuHs of the Session 1878. Baltimore. 



6. Hancock, A. On the Organisation of Brachiopoda. Trans. 



Bog. Soc. London. Vol. cxlviii. 1858. 



* Zeitschr. f. Wiss. Zool., Bd. xxvi. p. 393, footnote. 



