PHYSIOLOGY OF SYNAPTULA HYDRIFORMIS 335 



with Lesueur's and Oersted's West Indian species" (Clark, '07, 

 p. 83). Pourtales reports that when specimens of this species 

 were placed in a glass jar, they would climb along the sides 

 of the vessel by means of their tentacles, their bodies hanging 

 down in the water, and they seemed to adhere to the glass by 

 the outside surface of their tentacles. 



The body movements are much like those of the earthworm. 

 Indeed, the arrangement of the muscles is the same in both ani- 

 mals; circular muscles lie just beneath the epidermis, and longi- 

 tudinal muscles internal to the circular ones. At one phase of 

 the movement the circular muscles contract and the body of the 

 Synaptula is elongated. This is succeeded by a contraction of the 

 longitudinal muscles, following vonUexkull's ('00) rule whereby 

 the stretched muscle is the next to contract, which shortens the 

 body. Instead of setae, Synaptula has calcareous anchors, 

 which serve as fulcra when the animal is moving, or as very ef- 

 ficient hold-fasts when one attempts to remove a specimen from 

 sea-weed. Concerning the function of these peculiar structures, 

 which have their origin in the dermis, Selenka ('67) ventured to 

 suggest that they grew out beyond the subcuticula, bored through 

 the thin membranous outer skin, and aided the Synaptula in 

 clinging to the substrate. Semper ('68) on the contrary, claimed 

 that "ein solches Durchboren findet aber nie in natiirlichen Zus- 

 tanden statt," and he suggested a totally different function, 

 i.e., that of 'Tastorgane.' Nevertheless the anchors do project 

 beyond the epidermis and render it almost impossible to remove 

 a Synaptula from sea-weed without injury. In collecting speci- 

 mens, it was found best to break off a bit of sea-weed with an 

 animal clinging to it, rather than to attempt to pull the animal 

 away from the sea-weed. They even cling to one's- finger so 

 that it is with difficulty that they can be shaken off. 



Naturally anchors are of no avail when the animal is creeping 

 up the vertical surface of a smooth glass vessel. In this case the 

 whole outer glandular portion of the tentacles (cf. Pourtales, 

 '51), not merely the tips as in Rhabdomolgus ruber (Becher, 

 '07, p. 554), adheres to the surface along which the Synaptula 

 is moving. The longitudinal muscles of the tentacles contract, 



