On the Development of the Galcispongise. 41 



II. — On the Development of the, Calcispongige. 

 By Elias Metschnikoff*. 



[Plate II.] 



During my residence at Messina in the spring of 1868 I 

 made some observations on the development of Sycon ciliatum 

 {Sycandra raphanus. Hack.), which I have not hitherto pub- 

 lished, because I did not consider them sufficiently completef. 

 But now, since the appearance of Hiickel's ' Monograph of 

 the Calcispongia? 'J, I feel compelled to publish my investiga- 

 tions. The reasons which have moved me to hesitate no 

 longer in doing this will be clear enough from what follows. 



I hope that my memoir, small as it is, will not be passed 

 unnoticed by the readers of Hackel's three-volume monograph, 

 inasmuch as it is devoted exclusively to developmental history, 

 i. e. to that department of zoology the great importance of 

 which in morphological questions seems to be now generally 

 recognized. With regard to the special case before us, that 

 of the Calcispongia?, the important part of developmental 

 history is strongly insisted upon by Hackel ; but unfortunately 

 the investigations of that naturalist relating to this subject 

 are so defective that a fresh treatment of the matter has 

 become a pressing necessity. 



I pass now to the description of my investigations. When 

 we examine transverse sections of sexually mature Syca, 

 we observe beneath the entodermal lining a great number of 

 ova and embryos in very different stages of development. 

 The total and regular segmentation takes place in the same 

 way as is described by Hackel in Sycyssa Huxleyi and Leucul- 

 mis echinus. We have only to remark that a small so-called 

 segmentation-cavity (PI. II. fig. 2, c) is formed, which, how- 

 ever, soon disappears (fig. 3). As the result of the process 

 of segmentation a roundish embryo (fig. 4) is produced, on 

 which a great number of small cells are to be detected. I 

 could not succeed in discovering any process of differentiation 

 in the embryo, for which reason the question of the origin of 

 the germ-lamella? must remain undecided. Evidently the 

 stages are too quickly passed through for them to be accurately 

 observed. I must therefore pass on at once to the description 



* Translated by W. S. Dallas, F.L.S., from the ' Zeitschrift fur wissen- 

 schaftliche Zoologie,' Baud xxiv. (1874), pp. 1-14, pi. i. 



t I have already given a short account of them iu my annual report 

 upon the progress of developmental history, printed in Russian. 



\ f Die Kalkschwamme : eine Monographic.' 3 vols. Berlin, 1872. 

 In this paper I shall only quote the lirst volume of this work 



