52 JOURNAL OF CONCHOLOGY. 



foot and a swaying from side to side of the animal's body. The 

 latter act, as their name implies, by contractions, and only with 

 persistent waves of change passing along the nerves from the 

 ganglia to the fibres. The latter do not contract at all, but 

 become extended by a coagulation of their muscle-plasma 

 (myosin?) which begins at one end and advances along the 

 whole length of each fibre. This coagulation can only take 

 place when the lacunas of the pedal muscle are filled with 

 blood, and a single impulse from the pedal nerves is enough 

 to set it into action, after which it proceeds without the inter- 

 vention of any nervous agency. The other interesting item 

 is mentioned by A. Coutance (loc. cit.) who states that the 

 adductor muscle of Pecten is composed of two parts — one, 

 containing striated fibres ('muscular' part) and of a yellowish 

 colour ; the other, consisting of ordinary unstriped muscle-cells 

 ( ' ligamentous ' portion ) and bluish - white in colour. The 

 former portion, according to this author and H. von Ihering,^^ 

 closes the valves rapidly, the latter keeps them together when 

 closed, so that the muscle, as a whole, is never at rest. 



The pedal muscle of the snail can be thrown into a state 

 of tetanus — /. e. , the fusion of a series of successive contractions 

 into one continuous contraction — and here is another distinction 

 from vertebrate unstriped muscle which is incapable of passing 

 into a tetanic state of contraction. In this it resembles the 

 striated muscle of the higher animals. The number of stimuli 

 required in the case of the pedal muscle of the snail is ten per 

 second ; for the sake of comparison we may state that the wing- 

 muscles of insects require three hundred. 

 ♦-♦-♦ 



Limax flavus var. rufescens in West Lancashire. — 

 Mr. W. H. Heathcote sent me last week a half-grown example 

 of Limax flavus, which answers to Moquin's description of this 

 variety, taken in his wood-yard at Avenham Lane, Preston, 

 where the species is not uncommon. — W. Denison Roebuck. 



^^ Ueber Anomia. Z. Wiss, Zool., xxx Suppl. vol., pp. 13 — 27. 



J.C, vl., Jan., 18S9 



