WORMS. 



Fig. OS. — Metamorphosis of Phoronis. At A is shown the larva 

 with its whorl of tentacles (0 : and at p the internal pouch ; in Jl 

 the pouch is in process of eversion; in C the pouch (only pari 

 of which is shown) now forms the greater part of the body, tin- 

 tentacles and posterior extremity of the body (a) being drawn 

 close together. 



which is remarkable for the wonderful change it undergoes in the course of 

 its development. The young larva has a peculiar hood over the mouth, and 

 below this is a circle of ten- 

 tacles, while at the opposite 

 end of the body is the vent. 

 A peculiar pouch now be- 

 gins to grow inside of the 

 body ; and then, at what is 

 termed the critical period 

 (Fig. 68, B), this pouch 

 bursts forth and forms the 

 bulk of the bod} r of the 

 adult, while the mouth and 

 anal ends of the young are 

 drawn close to each other 

 as shown in Figure 68, C. 

 The process may almost be 

 summarized as a turning 

 inside out. 



The ' whale' s-tongue' worm (Balanoglossus) is also to be noticed. For 

 many years a peculiar larva was known which was supposed to be a young 

 starfish. Indeed, there was not the slightest doubt on the subject until 

 Metschnikoff, a Russian naturalist, and subsequently Mr. Alexander Agas- 

 siz, proved beyond a doubt that it was the larva of a very peculiar worm 

 comparatively common on our northern coast as well as on the shores of 

 the Mediterranean. The subject was supposed to be settled until, in 1883, 

 the development of another species occurring in North Carolina was stud- 

 ied. This, in its external appearance, closely resembled the more northern 

 form studied by Mr. Agassiz, but, strange to say, has an entirely different 

 life history. It does not have a metamorphosis ; there is no larval stage 

 suggestive of a young starfish, but the whole development is strikingly 

 like that of some of the lower vertebrates ! Where, in a systematic 

 arrangement of the animal kingdom, we shall place the ' whale's-tongue ' 

 is a question not yet decided. 



The rotifers or wheel-animalcules are another group the position of 

 which is not settled. At various times they have been placed among the 

 molluscs, the Crustacea, and the worms. It now seems probable that their 

 nearest relatives are to be found among annelid embryos, although in their 

 general appearance they differ widely from them. Wheel-animalcules are 

 very familiar objects to microscopists. They occur in both fresh and salt 

 water, but most abound in stagnant pools. In size they rarely exceed the 



