INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 419 



cuticle. The same process takes place in the adult under like 

 circumstances. So too in the epiphragms, with this difference, that 

 the spheres with concentric layers are mixed with granules poured 

 forth by the calcareous glands of the collar. The cicatrices of the 

 shell are produced even when the denuded part is immediately 

 covered over by a fragment corresiionding to that which had been 

 taken away. Fine plates of mica introduced between the shell and 

 the mantle are lined, on the internal surface, by a calcareous dei)osit. 



Molluscoida. 



Early Developmental Phenomena of the Salpae.* — The ovary 

 in these animals, Signor Todaro reminds us, lies in a blood-sinus of 

 the compound animal, which communicates with that of the rudimen- 

 tary uterus. On the side where the oviduct enters, which is the side 

 next to the respiratory chamber, the uterine wall is clothed with an 

 epithelium continuous with that which clothes that chamber. The 

 oviduct is solid, except where it traverses the uterine sinus. The 

 single ovum of tlie ovarian follicle has a large germinal vesicle with 

 a germinal spot sus2icnded by a protoplasmic network ; the nutritive 

 yolk is added subsequently in the form of globules of lecithin. 



The first changes which occur are the assumption of an oval form 

 by the ovum, and the departure of the germinal vesicle to the posterior 

 pole, where it disappears and is replaced by three, four, or five nuclei, 

 and a polar corpuscle which is ejected. With the breaking of the 

 chain, the follicle is brought near to the opening of the genital canal, 

 and fecundation takes place. The spermatic nucleus ai)pears directly 

 afterwards at the anterior pole, and the follicle passes into the uterine 

 sinus. It is uncertain what part the posterior nuclei play ; they dis- 

 appear in succession at this stage, and the spermatic nucleus also at 

 the same time. This appears first to have become the segmentation 

 nucleus, as its volume has become double of its original volume. 



Segmentation commences after the nuclei have gone ; after the 

 first cleavage, the follicular epithelial cells enlarge and develop nu- 

 cleated lecithin cells which arc thrust into the midst of the blasto- 

 derm cells, forming with them a solid mass. After segmentation the 

 wall of the follicle sends out a process which grows out and is almost 

 constricted otF; this connection becomes wide again, and the union of 

 the follicle with this diverticulum forms a cylindrical tube projecting 

 into the uterine sinus. Later, the follicle becomes round again ; it 

 then contains the morula, which consists of small blastoderm cells 

 aggregated into masses with the lecithin cells. 



The uterus now undergoes interesting changes. Its epithelial 

 and connective-tissue elements increase, and the latter give rise to 

 contractile cells; fnmi the margin of the epithelial layer a fold is 

 developed at the time of the outgrowth of the follicle, and, enclosing 

 some connective tissue, shuts olf from the respiratory chamber a 

 secondary chamber, the " epithelial uterine cavity," which is believed 

 to be homologous with the gravid mammalian uterus. The membrane 

 separating it from the uterus forms a di oiduu, distinguishable into u 



* ' Atti K. Acc'iJ. Liucii ' (Triiusuiit.), iv. (1880) p. SO. 



