ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 461 



The specimens observed of D. reiiculatum were seen to be im- 

 mature, not only from the fact that they were encapsuled, but from 

 the slight development of their generative organs. This species was, 

 however, seen to present many considerable deviations from the 

 ordinary type of Distomum ; it was of considerable size, being twice 

 that of the comparatively large JD. pulcherrimum of Weyenbergh. The 

 excretory vessels and the generative organs exhibit a remarkable 

 resemblance to those of Cestoda ; for the former have the terminal 

 vesicle greatly reduced, and the system of vessels is greatly branched, 

 while the arrangement of the anterior orifices calls to mind that 

 described by Fraipont in the Tetrarhynchi ; the uterus, moreover, is 

 simple and blind, and calls to mind the same organ in the Tseniidas. 



The author foresees that the Distomata will have to be broken up 

 into smaller groups, but he does not think (and the neglect of 

 Dujardin's classification supports his view) that any reasonable 

 method of classification is to be found in the number or arrangement 

 of the suckers. 



Development of Balanoglossus Kowalevskii, and the Afiinities 

 of the Enteropneusta.* — Mr. W. Bateson now gives an account of 

 the later stages in the development of Balanoglossus ; in the species 

 — J5. KowalevsJcii — which he examined there is no Tornaria-stage. 

 Shortly after hatching the transverse ring of cilia and the apical tuft 

 disappear ; the cilia on the body increase in size, and the tissues, 

 probably from the consumption of the yolk-particles, become more 

 transparent. A temporary organ in the form of a tail arises from the 

 posterior ventral surface, immediately below the anus. It is richly 

 provided with large glands, and serves as a strong sucker ; it atrophies 

 soon after the appearance of seven gill-slits, when the body is long 

 enough to be coiled round foreign objects. The mouth is directed 

 anteriorly ; in young specimens a rod of hypoblast, solid in front, is 

 gradually constricted off from the hypoblast in the dorsal middle 

 lino of the pharynx ; the cells of this rod gradually present an 

 appearance precisely comparable to that figured by Scott for the 

 notochord of young lampreys, and by Balfour for that of young 

 Elasmobranchs. The author regards it as comparable to, and hence- 

 forward speaks of it as a notochord ; " this view of its homology is 

 supported by the presence in the Enteropneusta of many other 

 structures pointing to vertebrate affinities." 



The nervous system has a canal and pore ; in the mode of origin 

 of the mesoblast, and the fate and asymmetry of the anterior coelomic 

 pouch, Balanoglossus resembles the Chordata, and especially the 

 Cephalochordata ; and the same is true of the atria and the excretory 

 funnels ; on the whole, the condition is that which would be produced 

 by a partial or arrested development of the corresponding structure 

 in AmpMoxus. The author regards Metschnikoffs view that the 

 branchial structures of Balanoglossus are comparable to the openings 

 from the body-cavity of Echinoderms as untenable ; and he comes to 

 the conclusion that the points of similarity with AmpMoxus are so 



* Proc, Koy. Soc, xxsviii. (1884) pp. 23-30. 



