xvii PKOTOCHOKDATA 609 



sessile forms which increase by budding. In one small sub-group, 

 the Ascidiae luciae, the colony has become free-swimming ; in 

 another sub-group, the Ascidiae simplices, the power of budding 

 has apparently never been acquired. If we compare the larvae of the 

 rest of the Ascidiacea, termed the Ascidiae compositae, with the 

 larvae of the Ascidiae simplices, we find that the former are dis- 

 tinguished from the latter by the precocious appearance of the 

 peculiar features of the adult. In other words, the Ascidiae simplices 

 preserve the larval stage in its most unmodified form, and it is to 

 them, therefore, that we turn in order to select a type for special 

 description. 



CYNTHIA 



The most recent work on the subject is by Couklin (1905), who 

 has followed the development of Cynthia, partita, cell for cell, until 

 the attainment of the larval form. He has done the same for dona 

 intestinalis, and for Phallusia (1911), and his researches have made 

 it probable that the same general scheme applies to all the Ascidiae 

 simplices. What is related for Cynthia will hold true, with slight 

 modifications, for the common simple Ascidiaus on the coasts of 

 England, and the work of Van Beneden and Julin (1884) makes it 

 clear that the development of ' Clavelina, the simplest form of the 

 Ascidiae compositae, follows the same general course, although, even 

 here, the telescoping of development, characteristic of compound 

 Ascidians, has begun to appear. 



Cynthia partita is an Ascidian found in abundance at Wood's 

 Hole. It lives fairly well in laboratory tanks, and it lays eggs in 

 the evening, which, in the course of about ten hours, develop into 

 fully organized free-swimming larvae. In order, therefore, to be able 

 to study the development by daylight, Conklin extracted eggs from 

 the ovary and artificially fertilized them in the morning. Of such 

 artificially fertilized eggs few developed, but these few were sufficient 

 to enable the development to be thoroughly investigated. In the 

 case of dona intestinalis, on the contrary, it is quite easy to artificially 

 fertilize the eggs if the sperm from another individual be used. The 

 animal's own sperm will not fertilize its eggs. 



The eggs of Cynthia were examined living, on a slide, in sea- water, 

 covered with a coverslip supported by fragments of coverslip about 

 i mm. thick. Under these circumstances the eggs could be rolled 

 about and examined from all sides. When it was desired to make 

 whole mounts, Kleinenberg's picro- sulphuric acid gave the best results. 

 The best method of staining was to use both Delafield's haematoxylin 

 and picric acid. The eggs are first stained with haematoxylin, and 

 this is differentiated in the usual way by adding acid alcohol ; then 

 for dehydration the alcohols of 90 per cent and absolute strength, 

 made yellow by the addition of picric acid crystals, are used. In this 

 way the mass of the egg is stained yellow, but the nuclei are stained 

 blue. For sections it was found best to preserve the eggs in picro-acetic 



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