302 SYNOPTIC COLLECTION. 



A worm that buries its long quill-shaped body with the 

 exception of a few of the anterior segments is Sabella 

 penicillus Linn. (No. 748, model). Its tube is leathery, and 

 is formed by a secretion of the body ; from its opening the 

 branching gills, which are supported by a cartilaginous 

 skeleton, are extended. The model shows the animal out 

 of its slender tube, so that the body with its setae and 

 parapodia as well as its long, delicate branchiae and 

 tentacles can be clearly seen. 



Many of these tube-inhabiting worms have large, seg- 

 mented bodies, while the paddles and setae are more or 

 less reduced in size. Such a worm is Spirographis 

 spallanzani (No. 749), in which- these lateral appendages 

 are tiny. The feelers, on the other hand, are active 

 working organs and are finely developed. 



Two tubes of Branchiomma koellikeri (No. 750), are 

 shown in No. 751. One is made of sand and tiny 

 pebbles; it is symmetrical and well put together. The 

 other is composed of similar materials throughout about 

 three fourths of its length, but the remaining fourth has 

 pieces of rock of surprising size incorporated in it. Its 

 extreme irregularity reminds one of the experimental 

 work in shell-making seen among the Protozoa (see 

 Saccammina, PI. 15), and sponges (Prophysema, PI. 60). 

 It is remarkable that the cementing material is sufficiently 

 strong to hold these fragments in place, especially as only 

 a small portion of their surface is in contact with the 

 tube. From the anterior end of the tube many delicate 

 tentacles are put forth. Along each side are short setae 

 without paddles. According to M'Intosh x one species of 

 this genus, Branchiomma vesiculosum, has the surface of 

 the greatly enlarged eye minutely dotted as if furnished 

 with corneal facets analogous to those of Crustacea and 

 Insecta ; the eye has proximally a kind of peduncle. 



The tubes already described have been formed mechani- 



1 Chall. Rep., Zool., XII, 1885, p. 494. 



