THE EMBRYONIC DEVELOPMENT OF THE SALPIDAE. 445 



cavity appears within each of the developing muscle-hoops and these 



,.; ivitu , s b ave been compared by S.yu-.ssky with those in the primitive 



muscle-plates of the Vertebrates (cavities of the primitrve segments). 



The elaeoblast (Fig. 224, eb) seems to be derived trom cells of the 



mesenchyme. ... 



The development of the other species of Salpa that are provided 



with the enveloping fold (S. africana, S. fusiformis and S. punctata) 



seems to follow essentially the same coarse as that of S. run,,,,, 

 Judgmg from the very fragmentary statements as to the ontogeny 

 of these forms (Babkois, No. 87, Salensky, No. 104), however, there 

 appears to be considerable variation in points of detail [see Heideb 

 (No. XIII.) and Kobotneff (Xos. XX., XX".. and XXIa.)J- 



General Considerations on the Embryonic Development of 



the Salpidae. 

 [The embryonic development of the Salpidae is still in spite of the recent 

 Jestigationsl of Bkooks, H EIDE k and Kobokhkkf, anything hut *££^ 

 understood The confusion arising from the immigration of the kalymmo- 

 eyts and the difficulty of discriminating between these cells and he ^smaller 

 Native blastomeres of Hkxbkk and Kobotn^, still requxres to be swept 

 aTy before we can make any satisfactory comparisons of the development of 

 SS whh that of other Tunicates. When, further, we compare the mono- 

 ■ .1 the two last authors with that of Bkooks, we must feel J that additional 

 onSmation of one or other of the views put forward by these writers! 

 nec^ry before one of them is finally accepted. It is obvious, however that 

 we are dealing with a highly specialised form of development which ha* 

 "iSin connection with the viviparous habit of Salpa and has been 



Ser , .plicated in connection with the peculiar life-history of tins form.], 



The embryo undergoes direct development in accordance with its 

 retention during the whole embryonic and larval periods Within the 

 Ullh of th e parent. We have already seen a similar omxssion of 

 metamorphosis among the Ascidiacea in the Molgulvlae. The Sal pi dae 

 i„ this respect show a more specialised condition in so far as the 

 embryo becomes closely connected with the tissues of the parent 

 !lu ,l a placenta develops for its nourishment, Since we may, with 

 some probability, derive the Salpida* from the attached Ascidia-like 

 forms we might be tempted to trace back the fixation of the embryo 

 ,„, thewa ll Of the respiratory cavity of the parent to this original 

 attached manner of life. 



[Considerable stress was formerly laid upon the °»^^^™ 

 described by Salensky as occurring in the various species of Salpa "peciallj 

 on the presence or absence of covering folds and on the structure of the 

 p Lel P According to *i». the covering folds were completely wantmg 



