ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 547 



bladder-like animal ought to do. The muscles appear to be unable to 

 give the animal the requisite consistence. 



In the cutis of Holothurians there are annular and longitudinal 

 fibres which have a muscular character. They may be regarded as 

 morphologically intermediate between connective-tissue and muscular 

 tissue. The hardening of the skin when irritated is due to a " tonic " 

 contraction of the muscle-like fibres in the cutis. It is a protection 

 against mechanical injury. In Aplysia and similar animals the harden- 

 ing is a necessary secondary result of contraction ; in Holothurians the 

 contraction is a necessary but unused secondary result of the hardening. 

 The skin has the tonus-function ; the true muscles have no tonus 

 function, but behave like skeletal muscles. In Gastropods and the 

 like the musculature has both a motor function and a tonus function. 

 The Holothurian skin may be compressed by the action of the muscles 

 proper ; the cutis fibres " lock " ; the muscles may relax without losing 

 what they have gained. The skin and muscles proper work together, 

 effecting the characteristic "Sperrung" without "Spannung." 



Fate of Middle Piece of Echinoid Spermatozoon.* — Fr. Meves 

 has followed the middle piece of the spermatozoon after fertilization in 

 the case of Parechiaus miliaris, and has found it persisting unchanged 

 on to the 32-cell stage. The recognition of this very minute body is 

 rendered possible by its peculiar ring-like shape. It is suggested that 

 the parts of the Pluteus larva which eventually come to nothing are 

 those which have no share in the middle piece of the spermatozoon, and 

 that the middle piece is carried on into those cells which form the 

 primordium of the sea-urchin proper. In any case, the author contends, 

 plastosome-substances from the male germ cell pass into -the embryo and 

 must not be excluded from the inheritance. 



Abnormal Sea-urchins.j — James Ritchie and J. A. Todd give an 

 account of the abnormal Echinoids in the collection of the Royal Scottish 

 Museum. A specimen of Amblypneustes ovum had ambulacrum iv 

 separated from the apical disk by about 1 cm. and showed no corre- 

 sponding ocular plate. A specimen of Echinus esculentus showed an 

 almost complete disappearance of ambulacrum v, and there was great 

 derangement and consequent regulation Another test of the same 

 species showed almost perfect hexamery. In this case we have to do 

 with a fundamental change in symmetry, doubtless congenital in origin, 

 and representing a duplication of parts. In the other cases the distortion 

 is due to incomplete development caused by. an interference with the 

 processes of growth. 



Crinoid Arms in Phylogeny.J — Elvira Wood has studied the arms 

 of several species of camerate Crinoids (Cactocrinus and Tehiocrinm) 

 with reference to the phylogenetic relations of the species. From the 

 proximal to the distal portion of the arm there may be observed a series 

 of changes which succeed one another in a definite order. These changes 



* Arch. Mikr. Anat., lxxxv. (1914) Heft 1, 2te AM., pp. 1-8 (2 pis.), 

 t Proc. R. Soc. Edinburgh, xxxiv. (1914) pp. 241-52 (1 pi. and 3 figs.). 

 \ Ann. New York Acad. Sci., xxiv. (1914) pp. 1-17 (5 pis.). 



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