Peripatus. 119 



the most gifted naturalists of his time, had the opportunity of Wall-case 

 dissecting freshly killed specimens at the Cape of Good Hope. (^^^ P^^" 



When opened under water a glistening appearance revealed 

 the presence of air-tul)es, such as are found among insects, spiders 

 and centipedes, and nowhere else in the animal kingdom ; hut, 

 whereas in these three groups the air-tuhes (or trachea^) are 

 supported hy a spiral coil of chitin which keeps them open after 

 preservation in spirit, those of Peripatus are not so supported. 



Fortunately also this Peripatus was viviparous, and, as the 

 anatomical drawing in the case shows, a number of eggs were 

 found in the oviduct ; these are in various stages of development : 

 following them out Moseley was able to see that the first of the 

 appendages are converted into mouth-organs. This is a character 

 which distinguishes the centipede from the ringed worm, and so far 

 settled the question of the relationship of Peripatus. But Moseley 

 did more than this, he showed that Peripatus belonged to that 

 division of the Arthropoda wdiich is known as Tracheata, and 

 which consists of scorpions, centipedes, flies and their allies. 

 During the last quarter of a century much attention has been 

 paid to the Onychopliora, of which more than 50 species are 

 now known. 



Peripatus is to be found in moist and shady places. It avoids 

 light, and is nocturnal in its habits. On irritation, it shoots out 

 tine threads of a tenacious milky fluid, not unlike the threads of a 

 spider's web. This fluid is sticky enough to hold fast flies. In 

 moving it never wriggles, but has a gait extremely like that of a 

 caterpillar. 



There are a number of more or less minute characters by 

 which the species are distinguished from one another. The most 

 remarkable difference perhaps is in the characters of their eggs. 

 In the Neotropical species, represented here by P. jidiformis, the 

 egg is minute, and almost entirely devoid of yolk. In the Cape 

 species (Peripatopsh ca pens is) the eggs are larger and there is 

 some yolk. In the eastern species (e.g., Eoperipatus horsti) the 

 egg is large, and there is a quantity of food-yolk. One at least of 

 the Australasian species lays eggs, which are hatched outside the 

 body. The species vary further in the number of legs, and also in 

 the constancy or inconstancy of the number ; that is to say, some 

 species have a definite number of legs, while others vary consider- 

 ably in the number that they possess. 



The group is of great scientific interest as a clear link between 

 Arthropods and Polychaete worms. 



