Prof. S. Loven on the Development of the Chitons. 413 



As already mentioned, Carter has observed peculiar bodies 

 in sponges, which he regards as spermatozoa. These agree in 

 no respect with the above ; they are much larger, and are fur- 

 nished with a contractile head, whilst the far smaller head of 

 the above-described spermatozoa never exhibits contractions. I 

 have found bodies during the winter in the sponges exactly 

 resembling Carter^s figures; these I can only regard as large 

 and small specimens of Trachelius trichophorus, the occurrence of 

 which in sponges Carter does not mention ; more rarely I found 

 a kind of Monad, probably identical with Dujardin^s Cercomonas 

 acuminata ; this differs, however, importantly from all the com- 

 ponents of sponges, in the presence of a contractile vesicle. On 

 the other hand, the spermatozoa which Huxley has figured as 

 those of Tethya closely resemble those of the Spongillse ; but 

 Huxley has said nothing about either their origin or their power 

 of motion. 



XXXIX. — 071 the Development of the Chitons. 

 By Prof. S. Loven*. 



When on a visit to our Western Skerries three years ago, I had 

 an opportunity of observing the development of Chiton margi- 

 natus, Pennant (C. cinereus, Linn., according to Forbes and 

 Hanley). 



Some individuals of this species, which were kept in confine- 

 ment, laid their eggs, loosely united in clusters of from seven to 

 sixteen, upon small stones. Each e^^ was furnished with an 

 envelope, which being folded, and as it were vesicular, was of 

 considerable thickness, amounting to about half the total radius. 

 All the stages of segmentation were already passed, and the 

 envelope contained a well-formed moving embryo (fig. 1). 



The embryo, 0*18 mill, in length, exactly of an oval form, and 

 without any trace of shell, is divided by a circular indentation 

 into two nearly equal parts ; and close to this indentation are 

 attached the cirri, by means of which the movements of the 

 embryo are effected. In the middle of the upper part there is 

 a tuft of very fine filaments, which scarcely exhibit any move- 

 ments. The lower half exhibits two dark points, one on each 

 side close to the indentation; these are the eyes, of which how- 

 ever only one is usually very distinct. The general form of the 

 animal is somewhat variable, the lower part sometimes giving 

 rise to a tapering process. The young ones, when freed, swim 



* Translated from Ofversigt af Kongl. Vetenskaps-Akademiens Forhand- 

 lingar, 1855, p. 169. 



