RECENT ADVANCES IN SCIENCE 643 



tion is subject to the influence of the nerve centres, as are 

 many other functional activities. In the same journal (Nov. 

 1 91 6) Parker and Titus treat of " The Structure of Metridium 

 (Actinobola) marginata Milne Edwards, with special reference 

 to its Neuro-Muscular Mechanism." They distinguish four 

 types of muscle cells with various relations to the nervous 

 system which itself is not limited to ectoderm or entoderm, but 

 penetrates the mesaglea and connects the two layers. Parker 

 (ibid.) describes four varieties of " The Effector Systems of 

 Actinians," the mucous, the nematocyst, the ciliary, and the 

 muscular. 



The polyzoa are treated by Lang in "A Revision of the 

 * Cribrimorph ' Cretaceous Polyzoa " (Ann and Mag. Nat. 

 Hist. July 1 91 6), and by Walters in " Some Species of Crisia " 

 (ibid. Dec. 1916). 



The " Factors affecting Male-production in Hydatina " 

 have been investigated by Shull and Ladoff (Jour. Exper. Zool. 

 July 1916), who find that various chemicals reduce male-pro- 

 duction and oxygen increases it. The results are not due to 

 osmotic pressure, acidity or alkalinity. 



The same journal contains accounts of the behaviour of 

 a sex chromosome complex in " The Germ Cells in Ascaris 

 incurvata " by Goodrich, and of the control of head produc- 

 tion in pieces of worm, viz. " Studies on the Dynamics of 

 Morphogenesis in Experimental Reproduction and Inheri- 

 tance : IX. The control of Head form and Head frequency in 

 Planaria by means of Potassium cyanide " by Child. In note 

 xxxix. from the Gatty Marine Laboratory M'Intosh treats of 

 11 Polychaetes " (Ann. and Mag. Nat. Hist. Aug. 1916). 



Clark writes " On New Starfish and five New Brittle Stars 

 from the Galapagos Islands " (ibid. July 191 6). The eggs of 

 the Echinodermata from their size, and ease with which they 

 can be manipulated, are favourite things for experimental 

 work and have been utilised in three papers. Doanchakoff in 

 " Studies on Cell Division and Cell Differentiation : I. Develop- 

 ment of the Cell Organs during the first Cleavage of the Sea- 

 urchin Egg " (Jour, of Morph. Sept. 191 6) claims that the differ- 

 ences exhibited by the most essential cell organs are easily 

 demonstrated. They appear regularly at definite stages of 

 cell mitosis and are to be regarded as the result of physico- 

 chemical cycles. Lillie in " The Physiology of Cell Division : VI. 



