PRIAPULUS AND HALICRYPTUS. 
199 
the same swiftness drawing it in again. Unless the little 
spikes were retractile I think they would be damaged in this 
process. In support of this view I may also mention a case 
where similar organs occur which have been observed in the 
act of being drawn in. I am alluding to the careful researches 
of Eisig 1 on the cup-shaped organs of the Capitellidse. He 
says, “ Die Basis des im iibrigen soliden Sinneshiigels ist mit 
einer kleinen Hohlung versehen, welche zunachst von den 
Wandungen des Hiigels, sodann aber von denjenigen des 
Hautmuskelschlauchs begrenzt, direct in die Perivisceralhohle 
iibergeht. An die Hiigel inseriren sich mehrere Muskeln, 
deren einer der Retractor, den freien Hiigel mehr oder weniger 
tief einzustiilpen vermag. Es ist der Druck des Blutstroms, 
der sowie den Russel und die Tentakel, auch das eingezogene 
Haarfeld wieder zur Ausstiilpung bringt.” 
The two special sets of muscles in the proboscis which have 
been mentioned above and which also occur in Halicryptus 
run underneath the rows of spikes, one on each side, and join 
the longitudinal muscles of the body wall in the trunk (fig. 
11, r. m.). 
Horst supposes that the above-mentioned hollow spaces are 
not without importance in the act of respiration. I have just 
stated my own view on this subject, and need not recur to it 
again. 
As regards the innervation of these organs I have not come 
to any definite results, although both osmic acid and chloride 
of gold were used. In some cases, indeed, I saw something 
like nerve-fibres at the base of a spike, but I was not able to 
positively prove that what I saw were really such. 
Saenger is quite determinate in his assertion that rings of 
nerves surround the body, one in every segment, similar to 
those discovered in Si pun cuius nudus. In pi. x, fig. 16, 
he has a drawing representing a lateral nerve going off from 
the nerve-cord, but as in his diagram the latter is separate 
from the hypodermis instead of lying inside it as a modifi- 
1 Eisig, “ Die Seitenorgane und beckeriormigen Organe der Capitelliden,” 
‘ Mitth. aus d. Zool. Station Neapel,’ vol. i, p. 280. 
VOL. XXV. NEW SER. 
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