KKPoKT ON TIIK TUXICATA. 9 



important papers corroborating Kowalevsky's results in all essential points, though 

 differing from him in some minor details. Kowalevsky has since published several 

 other embryological papers, chiefly extending his discoveries to other groups of the 

 Tunicata. 



Hancock took up the Ascidians of the British Seas, at first in conjunction with Alder, 

 who had already (1863) worked at the group. They described a number of new species, 

 and Hancock in 1868 published some of his anatomical observations in the Journal 

 of the Linnean Society. At the time of his death he was collecting material for a 

 Monograph upon the British Tunicata. 



In 1871-72 Verrill described a number of new species and genera of Ascidians from 

 the coasts of North America. 



In the following year Giard published a large work upon the Synascidia? containing the 

 descriptions of a considerable number of new species, and also many important anatomical 

 observations. About this time 0. Hertwig's paper on the structure of the test made its 

 appearance. This was by far the best paper that had yet appeared on this subject, and it 

 satisfactorily determined the structure of the different parts and their relations to one 

 another. The most important points have since been confirmed by Semper in his paper 

 on the presence of cellulose in the Ascidian test, published in 1875. A paper by B. 

 Hertwig, the brother of the above-named author, which also appeared in 1872, contains 

 a number of valuable anatomical observations, especially upon the structure of the 

 endostyle ; whfle, during the few years that had elapsed since Kowalevsky's and 

 Kupffer's first researches, many further details as to the embryology of Simple Ascidians, 

 and the process of gemmation in the Compound forms, had been obtained by the 

 investigations of Krohn, Metschnikoff, Kowalevsky, Stepanhoff, Kupffer, and others. 



At this time also (1872) an important memoir by H. Fol, upon the Appendiculariidse 

 of the Straits of Messina made its appearance. 



In 1874 Ussow's memoir upon the histology of the nerve ganglion and the neigh- 

 bouring organs was published in Russia. In this it is shown that the gland lying below 

 the ganglion has a duct which runs forwards to terminate in the so-called " olfactory 

 tubercle." 



In this same year Lacaze-Duthiers commenced the publication of his important work 

 upon the Ascidiaa Simplices of the coast of France. His first part was anatomical. A 

 species of Molgula was chosen as a type, and all its organs were described with great 

 thoroughness and minuteness. Lacaze-Duthiers, however, throughout regards the Ascidian 

 as a modified Lamellibranch mollusc. His second part, published a few years later 

 (1877), contains a systematic description of the family Molgulidse. He introduces two 

 new genera, Anurella and Ctenicella, of which the former differs from Molgida chiefly 

 in the fact that its embryos never develope into tailed larva?, but undergo a modified 

 process of development. The species are all described with great minuteness, and are 



(ZOOL. CHALL. EXP.-— PART XVII. — lSi^l'.) E 2 



