92 PROCEEDINGS OF THE ACADEMY OF [Jan. 



merite. Occasionally, also, it is the posterior part of the deutomerite 

 which is bent, the balance of the animal maintaining its original posi- 

 tion. Yet however varied these bendings may be, they are all of them 

 only contortions whereby the longitudinal axis loses its original straight- 

 ness. 



Their cause is contractions of the myocyte. It is easy to see how 

 such contortions could be produced by a shortening of the longitudinal 

 fibres of one side, possibly aided by a contraction of the transverse 

 fibres at the place where the bendings originate. This pull on the part 

 of the myocyte is resisted by the ectosarc to a greater or less extent, 

 contingent upon its rigidity and elasticity. This is shown by the sud- 

 denness with which the ectosarc springs back to its original position, 

 which presumably takes place when the pull exerted by the myocyte 

 ceases to act. The behavior of the ectosarc in such a case is, as previ- 

 ously stated, precisely what it would be were it composed of india- 

 rubber. 



The following point is also worthy of note. When a gregarine begins 

 to curve, one side is lengthened and the other shortened. The ecto- 

 sarc is evidently capable of a certain amount of contraction, since a 

 crescentic form may be assumed with the shortened side still presenting 

 a smooth contour. But if the bending be carried to any considerable 

 extent, the inner surface folds, the number and depth of these folds 

 depending upon the shape of the gregarine and the extent of the curva- 

 ture. This shows that the power of the ectosarc to contract is limited. 



A movement of the same general character as the bending is one 

 whereby the longitudinal axis is shortened. It consists in the pulling 

 of the protomerite into the deutomerite, as one may withdraw the 

 hand into the sleeve. I have noticed this in a number of species, 

 although it is by no means so frequently seen as the bending. It is 

 displayed indifferently by animals which are progressing and those 

 which are not. As in the case of the bending, the return to the typical 

 shape, in the elastic species, is by a sudden jerk. This movement is 

 explainable by a shortening of the longitudinal fibres around a given 

 zone of the animal's body. 



There is finally the so-called peristalsis. This, as defined by Delage 

 et Herouard (1896), consists of "Contractions peristaltiques, produites 

 par un etranglement transversal qui se propage le long du corps." It 

 does not, however, admit of quite so simple a definition. It may be a 

 swelling instead of a constriction. Further, it frequently happens that 

 instead of a series of such constrictions or swellings there will be but 

 one, which passes from the region of the septum to the posterior end 



