350 ZOOLOGY. 



The taxonomical deductions are that the Clifetognatha form a group 

 characterized, by the "body consisting of three segments, separated, by 

 septa and provided with horizontal fins; the head with prehensile 

 hooks, spines, and a 'cap,' with two eyes, and an unpaired olfactory 

 organ 5 ccelom spacious: the enterou has two mesenteries and opens 

 in front of the aventerous caudal segment; four longitudinal muscular 

 bands: nervous system consists of the ventral, the supra-oesophageal, 

 and the lateral cephalic ganglia: trunk segment with two ovaries; 

 caudal segment with two testes. — In this group are recognized two 

 modifications of generic value, one {Sagitta) having an unpaired caudal 

 and two pairs of lateral fins, including ten species, and the other 

 {Spadella) with an unpaired caudal fin and one i)air of lateral fins, in- 

 cluding three species. (Condensed from J. R. M. S., vol. iii, pp. 793-799.) 



PERIPATIDEA^^S. 



ON THE KELATIONS OF PERIPATUS. 



Until lately there has been no difficulty in trenchantly separating the 

 arthropods from the vermiform articulates, but in Peripatus (a terres- 

 trial worm-like animal of trojucal countries) we have a form that is at 

 once to some extent intermediate between the two, and that breaks 

 down the rigorous diagnoses of those great groups and forbids the neat- 

 ness and precision of definition former!}- accorded to them. On the one 

 hand Peripatus possesses quite a well-developed tracheal system and 

 therein agrees with the terrestrial arthropods. On the other hand it 

 agrees with the worms in that the segment at organs are in all essential 

 respects like those of the Vermes and especially of the leeches, each organ 

 consisting of a coiled glandular tube connected at one end with a short 

 tube of somewhat different character, and probably opening into the 

 body cavity, and at the other end dilating into a vesicle that debouches 

 on the surface of the body at the base of the corresponding foot. Mr. 

 Balfour has now called attention to a new feature in the economy of the 

 animal which throws some light on its relation shijis.* There is a glan<l 

 which has a duct opening into the mouth, and which is comparable with 

 the salivary gland of the centipedes. (It has. generally been considered 

 as a, " fat-body.") Now, salivary glands are distinctive of the Tiacheate 

 Arthropods, and are not at all represented in the worms ; we have there- 

 fore dn this structure of Peripatus another indication of its relationship 

 with the Arthropods. By recent authors Peripatus had been disting- 

 uished as the type of a i^rimary group under the name Protracheata, 

 and the data thus indicated are worthy of attention in connection with 

 its place in the system. 



* Balfour (F. M.) on certain points in the Anatomy of Periiiatus Capeusis. Proc. 

 Cambridge Phil. Soc, vol. iii, p. 6, 1879. 



